picom/src/backend/gl/gl_common.c

// SPDX-License-Identifier: MPL-2.0
// Copyright (c) Yuxuan Shui <yshuiv7@gmail.com>
#include <GL/gl.h>
#include <GL/glext.h>
#include <locale.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <xcb/render.h>        // for xcb_render_fixed_t, XXX

#include "common.h"
#include "compiler.h"
#include "config.h"
#include "kernel.h"
#include "log.h"
#include "region.h"
#include "string_utils.h"
#include "utils.h"

#include "backend/backend_common.h"
#include "backend/gl/gl_common.h"

#define GLSL(version, ...) "#version " #version "\n" #__VA_ARGS__
#define QUOTE(...) #__VA_ARGS__

static const GLuint vert_coord_loc = 0;
static const GLuint vert_in_texcoord_loc = 1;

struct gl_blur_context {
	enum blur_method method;
	gl_blur_shader_t *blur_shader;

	/// Temporary textures used for blurring. They are always the same size as the
	/// target, so they are always big enough without resizing.
	/// Turns out calling glTexImage to resize is expensive, so we avoid that.
	GLuint blur_texture[2];
	/// Temporary fbo used for blurring
	GLuint blur_fbo;

	int texture_width, texture_height;

	/// How much do we need to resize the damaged region for blurring.
	int resize_width, resize_height;

	int npasses;
};

static GLint glGetUniformLocationChecked(GLuint p, const char *name) {
	auto ret = glGetUniformLocation(p, name);
	if (ret < 0) {
		log_error("Failed to get location of uniform '%s'. compton might not "
		          "work correctly.",
		          name);
	}
	return ret;
}

GLuint gl_create_shader(GLenum shader_type, const char *shader_str) {
	log_trace("===\n%s\n===", shader_str);

	bool success = false;
	GLuint shader = glCreateShader(shader_type);
	if (!shader) {
		log_error("Failed to create shader with type %#x.", shader_type);
		goto end;
	}
	glShaderSource(shader, 1, &shader_str, NULL);
	glCompileShader(shader);

	// Get shader status
	{
		GLint status = GL_FALSE;
		glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
		if (GL_FALSE == status) {
			GLint log_len = 0;
			glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &log_len);
			if (log_len) {
				char log[log_len + 1];
				glGetShaderInfoLog(shader, log_len, NULL, log);
				log_error("Failed to compile shader with type %d: %s",
				          shader_type, log);
			}
			goto end;
		}
	}

	success = true;

end:
	if (shader && !success) {
		glDeleteShader(shader);
		shader = 0;
	}

	return shader;
}

GLuint gl_create_program(const GLuint *const shaders, int nshaders) {
	bool success = false;
	GLuint program = glCreateProgram();
	if (!program) {
		log_error("Failed to create program.");
		goto end;
	}

	for (int i = 0; i < nshaders; ++i)
		glAttachShader(program, shaders[i]);
	glLinkProgram(program);

	// Get program status
	{
		GLint status = GL_FALSE;
		glGetProgramiv(program, GL_LINK_STATUS, &status);
		if (GL_FALSE == status) {
			GLint log_len = 0;
			glGetProgramiv(program, GL_INFO_LOG_LENGTH, &log_len);
			if (log_len) {
				char log[log_len + 1];
				glGetProgramInfoLog(program, log_len, NULL, log);
				log_error("Failed to link program: %s", log);
			}
			goto end;
		}
	}
	success = true;

end:
	if (program) {
		for (int i = 0; i < nshaders; ++i)
			glDetachShader(program, shaders[i]);
	}
	if (program && !success) {
		glDeleteProgram(program);
		program = 0;
	}

	return program;
}

/**
 * @brief Create a program from vertex and fragment shader strings.
 */
GLuint gl_create_program_from_str(const char *vert_shader_str, const char *frag_shader_str) {
	GLuint vert_shader = 0;
	GLuint frag_shader = 0;
	GLuint prog = 0;

	if (vert_shader_str)
		vert_shader = gl_create_shader(GL_VERTEX_SHADER, vert_shader_str);
	if (frag_shader_str)
		frag_shader = gl_create_shader(GL_FRAGMENT_SHADER, frag_shader_str);

	{
		GLuint shaders[2];
		int count = 0;
		if (vert_shader) {
			shaders[count++] = vert_shader;
		}
		if (frag_shader) {
			shaders[count++] = frag_shader;
		}
		if (count) {
			prog = gl_create_program(shaders, count);
		}
	}

	if (vert_shader)
		glDeleteShader(vert_shader);
	if (frag_shader)
		glDeleteShader(frag_shader);

	return prog;
}

static void gl_free_prog_main(gl_win_shader_t *pprogram) {
	if (!pprogram)
		return;
	if (pprogram->prog) {
		glDeleteProgram(pprogram->prog);
		pprogram->prog = 0;
	}
}

/**
 * Render a region with texture data.
 *
 * @param ptex the texture
 * @param target the framebuffer to render into
 * @param dst_x,dst_y the top left corner of region where this texture
 *                    should go. In OpenGL coordinate system (important!).
 * @param reg_tgt     the clip region, in Xorg coordinate system
 * @param reg_visible ignored
 */
static void _gl_compose(backend_t *base, struct gl_image *img, GLuint target,
                        GLfloat *coord, GLuint *indices, int nrects) {

	struct gl_data *gd = (void *)base;
	if (!img || !img->inner->texture) {
		log_error("Missing texture.");
		return;
	}

	bool dual_texture = false;

	assert(gd->win_shader.prog);
	glUseProgram(gd->win_shader.prog);
	if (gd->win_shader.unifm_opacity >= 0) {
		glUniform1f(gd->win_shader.unifm_opacity, (float)img->opacity);
	}
	if (gd->win_shader.unifm_invert_color >= 0) {
		glUniform1i(gd->win_shader.unifm_invert_color, img->color_inverted);
	}
	if (gd->win_shader.unifm_tex >= 0) {
		glUniform1i(gd->win_shader.unifm_tex, 0);
	}
	if (gd->win_shader.unifm_dim >= 0) {
		glUniform1f(gd->win_shader.unifm_dim, (float)img->dim);
	}

	// log_trace("Draw: %d, %d, %d, %d -> %d, %d (%d, %d) z %d\n",
	//          x, y, width, height, dx, dy, ptex->width, ptex->height, z);

	// Bind texture
	glBindTexture(GL_TEXTURE_2D, img->inner->texture);
	if (dual_texture) {
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, img->inner->texture);
		glActiveTexture(GL_TEXTURE0);
	}

	GLuint vao;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	GLuint bo[2];
	glGenBuffers(2, bo);
	glBindBuffer(GL_ARRAY_BUFFER, bo[0]);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[1]);
	glBufferData(GL_ARRAY_BUFFER, (long)sizeof(*coord) * nrects * 16, coord, GL_STATIC_DRAW);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, (long)sizeof(*indices) * nrects * 6,
	             indices, GL_STATIC_DRAW);

	glEnableVertexAttribArray(vert_coord_loc);
	glEnableVertexAttribArray(vert_in_texcoord_loc);
	glVertexAttribPointer(vert_coord_loc, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4, NULL);
	glVertexAttribPointer(vert_in_texcoord_loc, 2, GL_FLOAT, GL_FALSE,
	                      sizeof(GLfloat) * 4, (void *)(sizeof(GLfloat) * 2));
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, target);
	glDrawElements(GL_TRIANGLES, nrects * 6, GL_UNSIGNED_INT, NULL);
	glDisableVertexAttribArray(vert_coord_loc);
	glDisableVertexAttribArray(vert_in_texcoord_loc);
	glBindVertexArray(0);
	glDeleteVertexArrays(1, &vao);

	// Cleanup
	glBindTexture(GL_TEXTURE_2D, 0);

	if (dual_texture) {
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, 0);
		glActiveTexture(GL_TEXTURE0);
	}

	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
	glDeleteBuffers(2, bo);

	glUseProgram(0);

	gl_check_err();

	return;
}

/// Convert rectangles in X coordinates to OpenGL vertex and texture coordinates
/// @param[in] nrects, rects   rectangles
/// @param[in] dst_x, dst_y    origin of the OpenGL texture, affect the calculated texture
///                            coordinates
/// @param[in] width, height   size of the OpenGL texture
/// @param[in] root_height     height of the back buffer
/// @param[in] y_inverted      whether the texture is y inverted
/// @param[out] coord, indices output
static void x_rect_to_coords(int nrects, const rect_t *rects, int dst_x, int dst_y,
                             int width, int height, int root_height, bool y_inverted,
                             GLfloat *coord, GLuint *indices) {
	dst_y = root_height - dst_y;
	if (y_inverted) {
		dst_y -= height;
	}

	for (int i = 0; i < nrects; i++) {
		// Y-flip. Note after this, crect.y1 > crect.y2
		rect_t crect = rects[i];
		crect.y1 = root_height - crect.y1;
		crect.y2 = root_height - crect.y2;

		// Calculate texture coordinates
		// (texture_x1, texture_y1), texture coord for the _bottom left_ corner
		auto texture_x1 = (GLfloat)(crect.x1 - dst_x);
		auto texture_y1 = (GLfloat)(crect.y2 - dst_y);
		auto texture_x2 = texture_x1 + (GLfloat)(crect.x2 - crect.x1);
		auto texture_y2 = texture_y1 + (GLfloat)(crect.y1 - crect.y2);

		// X pixmaps might be Y inverted, invert the texture coordinates
		if (y_inverted) {
			texture_y1 = (GLfloat)height - texture_y1;
			texture_y2 = (GLfloat)height - texture_y2;
		}

		// GL_TEXTURE_2D coordinates are normalized
		// TODO use texelFetch
		texture_x1 /= (GLfloat)width;
		texture_y1 /= (GLfloat)height;
		texture_x2 /= (GLfloat)width;
		texture_y2 /= (GLfloat)height;

		// Vertex coordinates
		auto vx1 = (GLfloat)crect.x1;
		auto vy1 = (GLfloat)crect.y2;
		auto vx2 = (GLfloat)crect.x2;
		auto vy2 = (GLfloat)crect.y1;

		// log_trace("Rect %d: %f, %f, %f, %f -> %d, %d, %d, %d",
		//          ri, rx, ry, rxe, rye, rdx, rdy, rdxe, rdye);

		memcpy(&coord[i * 16],
		       (GLfloat[][2]){
		           {vx1, vy1},
		           {texture_x1, texture_y1},
		           {vx2, vy1},
		           {texture_x2, texture_y1},
		           {vx2, vy2},
		           {texture_x2, texture_y2},
		           {vx1, vy2},
		           {texture_x1, texture_y2},
		       },
		       sizeof(GLfloat[2]) * 8);

		GLuint u = (GLuint)(i * 4);
		memcpy(&indices[i * 6], (GLuint[]){u + 0, u + 1, u + 2, u + 2, u + 3, u + 0},
		       sizeof(GLuint) * 6);
	}
}

void gl_compose(backend_t *base, void *image_data, int dst_x, int dst_y,
                const region_t *reg_tgt, const region_t *reg_visible) {
	struct gl_data *gd = (void *)base;
	struct gl_image *img = image_data;

	// Painting
	int nrects;
	const rect_t *rects;
	rects = pixman_region32_rectangles((region_t *)reg_tgt, &nrects);
	if (!nrects) {
		// Nothing to paint
		return;
	}

	// Until we start to use glClipControl, reg_tgt, dst_x and dst_y and
	// in a different coordinate system than the one OpenGL uses.
	// OpenGL window coordinate (or NDC) has the origin at the lower left of the
	// screen, with y axis pointing up; Xorg has the origin at the upper left of the
	// screen, with y axis pointing down. We have to do some coordinate conversion in
	// this function

	auto coord = ccalloc(nrects * 16, GLfloat);
	auto indices = ccalloc(nrects * 6, GLuint);
	x_rect_to_coords(nrects, rects, dst_x, dst_y, img->inner->width, img->inner->height,
	                 gd->height, img->inner->y_inverted, coord, indices);
	_gl_compose(base, img, 0, coord, indices, nrects);

	free(indices);
	free(coord);
}

/**
 * Blur contents in a particular region.
 */
bool gl_blur(backend_t *base, double opacity, void *ctx, const region_t *reg_blur,
             const region_t *reg_visible) {
	struct gl_blur_context *bctx = ctx;
	struct gl_data *gd = (void *)base;

	if (gd->width + bctx->resize_width * 2 != bctx->texture_width ||
	    gd->height + bctx->resize_height * 2 != bctx->texture_height) {
		// Resize the temporary textures used for blur in case the root
		// size changed
		bctx->texture_width = gd->width + bctx->resize_width * 2;
		bctx->texture_height = gd->height + bctx->resize_height * 2;

		glBindTexture(GL_TEXTURE_2D, bctx->blur_texture[0]);
		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, bctx->texture_width,
		             bctx->texture_height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);
		if (bctx->npasses > 1) {
			glBindTexture(GL_TEXTURE_2D, bctx->blur_texture[1]);
			glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, bctx->texture_width,
			             bctx->texture_height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);
		}

		// XXX: do we need projection matrix for blur at all?
		// Note: OpenGL matrices are column major
		GLfloat projection_matrix[4][4] = {
		    {2.0f / (GLfloat)bctx->texture_width, 0, 0, 0},
		    {0, 2.0f / (GLfloat)bctx->texture_height, 0, 0},
		    {0, 0, 0, 0},
		    {-1, -1, 0, 1}};

		// Update projection matrices in the blur shaders
		for (int i = 0; i < bctx->npasses - 1; i++) {
			assert(bctx->blur_shader[i].prog);
			glUseProgram(bctx->blur_shader[i].prog);
			int pml = glGetUniformLocationChecked(bctx->blur_shader[i].prog,
			                                      "projection");
			glUniformMatrix4fv(pml, 1, false, projection_matrix[0]);
		}

		GLfloat projection_matrix2[4][4] = {{2.0f / (GLfloat)gd->width, 0, 0, 0},
		                                    {0, 2.0f / (GLfloat)gd->height, 0, 0},
		                                    {0, 0, 0, 0},
		                                    {-1, -1, 0, 1}};
		assert(bctx->blur_shader[bctx->npasses - 1].prog);
		glUseProgram(bctx->blur_shader[bctx->npasses - 1].prog);
		int pml = glGetUniformLocationChecked(
		    bctx->blur_shader[bctx->npasses - 1].prog, "projection");
		glUniformMatrix4fv(pml, 1, false, projection_matrix2[0]);
	}

	// Remainder: regions are in Xorg coordinates
	auto reg_blur_resized =
	    resize_region(reg_blur, bctx->resize_width, bctx->resize_height);
	const rect_t *extent = pixman_region32_extents((region_t *)reg_blur),
	             *extent_resized = pixman_region32_extents(&reg_blur_resized);
	int width = extent->x2 - extent->x1, height = extent->y2 - extent->y1,
	    width_resized = extent_resized->x2 - extent_resized->x1,
	    height_resized = extent_resized->y2 - extent_resized->y1;
	int dst_y_resized_screen_coord = gd->height - extent_resized->y2,
	    dst_y_resized_fb_coord = bctx->texture_height - extent_resized->y2;
	if (width == 0 || height == 0) {
		return true;
	}

	bool ret = false;
	int nrects, nrects_resized;
	const rect_t *rects = pixman_region32_rectangles((region_t *)reg_blur, &nrects),
	             *rects_resized =
	                 pixman_region32_rectangles(&reg_blur_resized, &nrects_resized);
	if (!nrects || !nrects_resized) {
		return true;
	}

	auto coord = ccalloc(nrects * 16, GLfloat);
	auto indices = ccalloc(nrects * 6, GLuint);
	x_rect_to_coords(nrects, rects, extent_resized->x1, extent_resized->y2,
	                 bctx->texture_width, bctx->texture_height, gd->height, false,
	                 coord, indices);

	auto coord_resized = ccalloc(nrects_resized * 16, GLfloat);
	auto indices_resized = ccalloc(nrects_resized * 6, GLuint);
	x_rect_to_coords(nrects_resized, rects_resized, extent_resized->x1,
	                 extent_resized->y2, bctx->texture_width, bctx->texture_height,
	                 bctx->texture_height, false, coord_resized, indices_resized);
	pixman_region32_fini(&reg_blur_resized);

	GLuint vao[2];
	glGenVertexArrays(2, vao);
	GLuint bo[4];
	glGenBuffers(4, bo);

	glBindVertexArray(vao[0]);
	glBindBuffer(GL_ARRAY_BUFFER, bo[0]);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[1]);
	glBufferData(GL_ARRAY_BUFFER, (long)sizeof(*coord) * nrects * 16, coord, GL_STATIC_DRAW);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, (long)sizeof(*indices) * nrects * 6,
	             indices, GL_STATIC_DRAW);
	glEnableVertexAttribArray(vert_coord_loc);
	glEnableVertexAttribArray(vert_in_texcoord_loc);
	glVertexAttribPointer(vert_coord_loc, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4, NULL);
	glVertexAttribPointer(vert_in_texcoord_loc, 2, GL_FLOAT, GL_FALSE,
	                      sizeof(GLfloat) * 4, (void *)(sizeof(GLfloat) * 2));

	glBindVertexArray(vao[1]);
	glBindBuffer(GL_ARRAY_BUFFER, bo[2]);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[3]);
	glBufferData(GL_ARRAY_BUFFER, (long)sizeof(*coord_resized) * nrects_resized * 16,
	             coord_resized, GL_STATIC_DRAW);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER,
	             (long)sizeof(*indices_resized) * nrects_resized * 6, indices_resized,
	             GL_STATIC_DRAW);
	glEnableVertexAttribArray(vert_coord_loc);
	glEnableVertexAttribArray(vert_in_texcoord_loc);
	glVertexAttribPointer(vert_coord_loc, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 4, NULL);
	glVertexAttribPointer(vert_in_texcoord_loc, 2, GL_FLOAT, GL_FALSE,
	                      sizeof(GLfloat) * 4, (void *)(sizeof(GLfloat) * 2));

	int curr = 0;
	glReadBuffer(GL_BACK);
	glBindTexture(GL_TEXTURE_2D, bctx->blur_texture[0]);
	// Copy the area to be blurred into tmp buffer

	int copy_tex_xoffset = 0, copy_tex_yoffset = 0, copy_tex_x = extent_resized->x1,
	    copy_tex_y = dst_y_resized_screen_coord;
	glCopyTexSubImage2D(GL_TEXTURE_2D, 0, copy_tex_xoffset, copy_tex_yoffset,
	                    copy_tex_x, copy_tex_y, width_resized, height_resized);

	for (int i = 0; i < bctx->npasses; ++i) {
		const gl_blur_shader_t *p = &bctx->blur_shader[i];
		assert(p->prog);

		assert(bctx->blur_texture[curr]);
		glBindTexture(GL_TEXTURE_2D, bctx->blur_texture[curr]);

		glUseProgram(p->prog);
		if (i < bctx->npasses - 1) {
			// not last pass, draw into framebuffer, with resized regions
			glBindVertexArray(vao[1]);
			glBindFramebuffer(GL_DRAW_FRAMEBUFFER, bctx->blur_fbo);

			glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
			                       GL_TEXTURE_2D, bctx->blur_texture[!curr], 0);
			glDrawBuffer(GL_COLOR_ATTACHMENT0);
			if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
				log_error("Framebuffer attachment failed.");
				goto end;
			}
			glUniform1f(p->unifm_opacity, 1.0);
			// For other than last pass, we are drawing to a texture, we
			// translate the render origin so we don't need a big texture
			glUniform2f(p->orig_loc, -(GLfloat)extent_resized->x1,
			            -(GLfloat)dst_y_resized_fb_coord);
			glViewport(0, 0, bctx->texture_width, bctx->texture_height);
		} else {
			// last pass, draw directly into the back buffer, with origin
			// regions
			glBindVertexArray(vao[0]);
			glBindFramebuffer(GL_FRAMEBUFFER, 0);
			glDrawBuffer(GL_BACK);
			glUniform1f(p->unifm_opacity, (float)opacity);
			glUniform2f(p->orig_loc, 0, 0);
			glViewport(0, 0, gd->width, gd->height);
		}

		if (p->unifm_offset_x >= 0) {
			glUniform1f(p->unifm_offset_x, 1.0f / (GLfloat)bctx->texture_width);
		}
		if (p->unifm_offset_y >= 0) {
			glUniform1f(p->unifm_offset_y, 1.0f / (GLfloat)bctx->texture_height);
		}
		glDrawElements(GL_TRIANGLES, nrects * 6, GL_UNSIGNED_INT, NULL);

		// XXX use multiple draw calls is probably going to be slow than
		//     just simply blur the whole area.

		curr = !curr;
	}

	ret = true;

end:
	glBindFramebuffer(GL_FRAMEBUFFER, 0);
	glBindTexture(GL_TEXTURE_2D, 0);
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
	glDeleteBuffers(4, bo);
	glBindVertexArray(0);
	glDeleteVertexArrays(2, vao);

	free(indices);
	free(coord);
	free(indices_resized);
	free(coord_resized);

	gl_check_err();

	return ret;
}

// clang-format off
const char *vertex_shader = GLSL(330,
	uniform mat4 projection;
	uniform vec2 orig;
	layout(location = 0) in vec2 coord;
	layout(location = 1) in vec2 in_texcoord;
	out vec2 texcoord;
	void main() {
		gl_Position = projection * vec4(coord + orig, 0, 1);
		texcoord = in_texcoord;
	}
);
// clang-format on

/**
 * Load a GLSL main program from shader strings.
 */
static int gl_win_shader_from_string(const char *vshader_str, const char *fshader_str,
                                     gl_win_shader_t *ret) {
	// Build program
	ret->prog = gl_create_program_from_str(vshader_str, fshader_str);
	if (!ret->prog) {
		log_error("Failed to create GLSL program.");
		return -1;
	}

	// Get uniform addresses
	ret->unifm_opacity = glGetUniformLocationChecked(ret->prog, "opacity");
	ret->unifm_invert_color = glGetUniformLocationChecked(ret->prog, "invert_color");
	ret->unifm_tex = glGetUniformLocationChecked(ret->prog, "tex");
	ret->unifm_dim = glGetUniformLocationChecked(ret->prog, "dim");

	glUseProgram(ret->prog);
	int orig_loc = glGetUniformLocation(ret->prog, "orig");
	glUniform2f(orig_loc, 0, 0);

	gl_check_err();

	return true;
}

/**
 * Callback to run on root window size change.
 */
void gl_resize(struct gl_data *gd, int width, int height) {
	glViewport(0, 0, width, height);
	gd->height = height;
	gd->width = width;

	// XXX: do we need projection matrix at all?
	// Note: OpenGL matrices are column major
	GLfloat projection_matrix[4][4] = {{2.0f / (GLfloat)width, 0, 0, 0},
	                                   {0, 2.0f / (GLfloat)height, 0, 0},
	                                   {0, 0, 0, 0},
	                                   {-1, -1, 0, 1}};

	// Update projection matrix in the win shader
	glUseProgram(gd->win_shader.prog);
	int pml = glGetUniformLocationChecked(gd->win_shader.prog, "projection");
	glUniformMatrix4fv(pml, 1, false, projection_matrix[0]);

	glUseProgram(gd->fill_shader.prog);
	pml = glGetUniformLocationChecked(gd->fill_shader.prog, "projection");
	glUniformMatrix4fv(pml, 1, false, projection_matrix[0]);

	gl_check_err();
}

// clang-format off
static const char fill_frag[] = GLSL(330,
	uniform vec4 color;
	void main() {
		gl_FragColor = color;
	}
);

static const char fill_vert[] = GLSL(330,
	layout(location = 0) in vec2 in_coord;
	uniform mat4 projection;
	void main() {
		gl_Position = projection * vec4(in_coord, 0, 1);
	}
);
// clang-format on

/// Fill a given region in bound framebuffer.
/// @param[in] y_inverted whether the y coordinates in `clip` should be inverted
static void
_gl_fill(backend_t *base, struct color c, const region_t *clip, int height, bool y_inverted) {
	static const GLuint fill_vert_in_coord_loc = 0;
	int nrects;
	const rect_t *rect = pixman_region32_rectangles((region_t *)clip, &nrects);
	struct gl_data *gd = (void *)base;

	GLuint vao;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);

	GLuint bo[2];
	glGenBuffers(2, bo);
	glUseProgram(gd->fill_shader.prog);
	glUniform4f(gd->fill_shader.color_loc, (GLfloat)c.red, (GLfloat)c.green,
	            (GLfloat)c.blue, (GLfloat)c.alpha);
	glEnableVertexAttribArray(fill_vert_in_coord_loc);
	glBindBuffer(GL_ARRAY_BUFFER, bo[0]);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[1]);

	auto coord = ccalloc(nrects * 8, GLint);
	auto indices = ccalloc(nrects * 6, GLuint);
	for (int i = 0; i < nrects; i++) {
		GLint y1 = y_inverted ? height - rect[i].y2 : rect[i].y1,
		      y2 = y_inverted ? height - rect[i].y1 : rect[i].y2;
		memcpy(&coord[i * 8],
		       (GLint[][2]){
		           {rect[i].x1, y1}, {rect[i].x2, y1}, {rect[i].x2, y2}, {rect[i].x1, y2}},
		       sizeof(GLint[2]) * 4);
		indices[i * 6 + 0] = (GLuint)i * 4 + 0;
		indices[i * 6 + 1] = (GLuint)i * 4 + 1;
		indices[i * 6 + 2] = (GLuint)i * 4 + 2;
		indices[i * 6 + 3] = (GLuint)i * 4 + 2;
		indices[i * 6 + 4] = (GLuint)i * 4 + 3;
		indices[i * 6 + 5] = (GLuint)i * 4 + 0;
	}
	glBufferData(GL_ARRAY_BUFFER, nrects * 8 * (long)sizeof(*coord), coord, GL_STREAM_DRAW);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, nrects * 6 * (long)sizeof(*indices),
	             indices, GL_STREAM_DRAW);

	glVertexAttribPointer(fill_vert_in_coord_loc, 2, GL_INT, GL_FALSE,
	                      sizeof(*coord) * 2, (void *)0);
	glDrawElements(GL_TRIANGLES, nrects * 6, GL_UNSIGNED_INT, NULL);
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
	glDisableVertexAttribArray(fill_vert_in_coord_loc);
	glBindVertexArray(0);
	glDeleteVertexArrays(1, &vao);

	glDeleteBuffers(2, bo);
}

void gl_fill(backend_t *base, struct color c, const region_t *clip) {
	struct gl_data *gd = (void *)base;
	return _gl_fill(base, c, clip, gd->height, true);
}

void gl_release_image(backend_t *base, void *image_data) {
	struct gl_image *wd = image_data;
	struct gl_data *gl = (void *)base;
	wd->inner->refcount--;
	assert(wd->inner->refcount >= 0);
	if (wd->inner->refcount > 0) {
		free(wd);
		return;
	}

	gl->release_user_data(base, wd->inner);
	assert(wd->inner->user_data == NULL);

	glDeleteTextures(1, &wd->inner->texture);
	free(wd->inner);
	free(wd);
	gl_check_err();
}

void *gl_copy(backend_t *base, const void *image_data, const region_t *reg_visible) {
	const struct gl_image *img = image_data;
	auto new_img = ccalloc(1, struct gl_image);
	*new_img = *img;
	new_img->inner->refcount++;
	return new_img;
}

static inline void gl_free_blur_shader(gl_blur_shader_t *shader) {
	if (shader->prog) {
		glDeleteProgram(shader->prog);
	}

	shader->prog = 0;
}

void gl_destroy_blur_context(backend_t *base, void *ctx) {
	struct gl_blur_context *bctx = ctx;
	// Free GLSL shaders/programs
	for (int i = 0; i < bctx->npasses; ++i) {
		gl_free_blur_shader(&bctx->blur_shader[i]);
	}
	free(bctx->blur_shader);

	glDeleteTextures(bctx->npasses > 1 ? 2 : 1, bctx->blur_texture);
	if (bctx->npasses > 1) {
		glDeleteFramebuffers(1, &bctx->blur_fbo);
	}
	free(bctx);

	gl_check_err();
}

/**
 * Initialize GL blur filters.
 */
void *gl_create_blur_context(backend_t *base, enum blur_method method, void *args) {
	bool success = true;
	auto gd = (struct gl_data *)base;

	struct conv **kernels;
	auto ctx = ccalloc(1, struct gl_blur_context);

	if (!method || method >= BLUR_METHOD_INVALID) {
		ctx->method = BLUR_METHOD_NONE;
		return ctx;
	}

	ctx->method = BLUR_METHOD_KERNEL;
	if (method == BLUR_METHOD_KERNEL) {
		ctx->npasses = ((struct kernel_blur_args *)args)->kernel_count;
		kernels = ((struct kernel_blur_args *)args)->kernels;
	} else {
		kernels = generate_blur_kernel(method, args, &ctx->npasses);
	}

	if (!ctx->npasses) {
		ctx->method = BLUR_METHOD_NONE;
		return ctx;
	}

	ctx->blur_shader = ccalloc(ctx->npasses, gl_blur_shader_t);

	char *lc_numeric_old = strdup(setlocale(LC_NUMERIC, NULL));
	// Enforce LC_NUMERIC locale "C" here to make sure decimal point is sane
	// Thanks to hiciu for reporting.
	setlocale(LC_NUMERIC, "C");

	// clang-format off
	static const char *FRAG_SHADER_BLUR = GLSL(330,
		%s\n // other extension pragmas
		uniform float offset_x;
		uniform float offset_y;
		uniform sampler2D tex_scr;
		uniform float opacity;
		in vec2 texcoord;
		out vec4 out_color;
		void main() {
			vec4 sum = vec4(0.0, 0.0, 0.0, 0.0);
			%s //body of the convolution
			out_color = sum / float(%.7g) * opacity;
		}
	);
	static const char *FRAG_SHADER_BLUR_ADD = QUOTE(
		sum += float(%.7g) *
		       texture2D(tex_scr, vec2(texcoord.x + offset_x * float(%d),
		                               texcoord.y + offset_y * float(%d)));
	);
	// clang-format on

	const char *shader_add = FRAG_SHADER_BLUR_ADD;
	char *extension = strdup("");

	for (int i = 0; i < ctx->npasses; i++) {
		auto kern = kernels[i];
		// Build shader
		int width = kern->w, height = kern->h;
		int nele = width * height;
		size_t body_len = (strlen(shader_add) + 42) * (uint)nele;
		char *shader_body = ccalloc(body_len, char);
		char *pc = shader_body;

		double sum = 0.0;
		for (int j = 0; j < height; ++j) {
			for (int k = 0; k < width; ++k) {
				double val;
				val = kern->data[j * width + k];
				if (val == 0) {
					continue;
				}
				sum += val;
				pc += snprintf(pc, body_len - (ulong)(pc - shader_body),
				               FRAG_SHADER_BLUR_ADD, val, k - width / 2,
				               j - height / 2);
				assert(pc < shader_body + body_len);
			}
		}

		auto pass = ctx->blur_shader + i;
		size_t shader_len = strlen(FRAG_SHADER_BLUR) + strlen(extension) +
		                    strlen(shader_body) + 10 /* sum */ +
		                    1 /* null terminator */;
		char *shader_str = ccalloc(shader_len, char);
		auto real_shader_len = snprintf(shader_str, shader_len, FRAG_SHADER_BLUR,
		                                extension, shader_body, sum);
		CHECK(real_shader_len >= 0);
		CHECK((size_t)real_shader_len < shader_len);
		free(shader_body);

		// Build program
		pass->prog = gl_create_program_from_str(vertex_shader, shader_str);
		free(shader_str);
		if (!pass->prog) {
			log_error("Failed to create GLSL program.");
			success = false;
			goto out;
		}
		glBindFragDataLocation(pass->prog, 0, "out_color");

		// Get uniform addresses
		pass->unifm_offset_x =
		    glGetUniformLocationChecked(pass->prog, "offset_x");
		pass->unifm_offset_y =
		    glGetUniformLocationChecked(pass->prog, "offset_y");
		pass->unifm_opacity = glGetUniformLocationChecked(pass->prog, "opacity");
		pass->orig_loc = glGetUniformLocationChecked(pass->prog, "orig");
		ctx->resize_width += kern->w / 2;
		ctx->resize_height += kern->h / 2;
	}

	// Texture size will be defined by gl_resize
	glGenTextures(ctx->npasses > 1 ? 2 : 1, ctx->blur_texture);
	glBindTexture(GL_TEXTURE_2D, ctx->blur_texture[0]);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	if (ctx->npasses > 1) {
		glBindTexture(GL_TEXTURE_2D, ctx->blur_texture[1]);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
		glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
		// Generate FBO and textures when needed
		glGenFramebuffers(1, &ctx->blur_fbo);
		if (!ctx->blur_fbo) {
			log_error("Failed to generate framebuffer object for blur");
			success = false;
			goto out;
		}
	}

out:
	if (method != BLUR_METHOD_KERNEL) {
		// We generated the blur kernels, so we need to free them
		for (int i = 0; i < ctx->npasses; i++) {
			free(kernels[i]);
		}
		free(kernels);
	}

	if (!success) {
		gl_destroy_blur_context(&gd->base, ctx);
		ctx = NULL;
	}

	free(extension);
	// Restore LC_NUMERIC
	setlocale(LC_NUMERIC, lc_numeric_old);
	free(lc_numeric_old);

	gl_check_err();
	return ctx;
}

// clang-format off
const char *win_shader_glsl = GLSL(330,
	uniform float opacity;
	uniform float dim;
	uniform bool invert_color;
	in vec2 texcoord;
	uniform sampler2D tex;

	void main() {
		vec4 c = texture2D(tex, texcoord.xy);
		if (invert_color) {
			c = vec4(c.aaa - c.rgb, c.a);
		}
		c = vec4(c.rgb * (1.0 - dim), c.a) * opacity;
		gl_FragColor = c;
	}
);
// clang-format on

bool gl_init(struct gl_data *gd, session_t *ps) {
	// Initialize GLX data structure
	glDisable(GL_DEPTH_TEST);
	glDepthMask(GL_FALSE);

	glEnable(GL_BLEND);
	// X pixmap is in premultiplied alpha, so we might just as well use it too.
	// Thanks to derhass for help.
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

	// Initialize stencil buffer
	glDisable(GL_STENCIL_TEST);
	glStencilMask(0x1);
	glStencilFunc(GL_EQUAL, 0x1, 0x1);

	// Clear screen
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
	glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

	gl_win_shader_from_string(vertex_shader, win_shader_glsl, &gd->win_shader);
	gd->fill_shader.prog = gl_create_program_from_str(fill_vert, fill_frag);
	gd->fill_shader.color_loc = glGetUniformLocation(gd->fill_shader.prog, "color");

	// Set up the size of the viewport. We do this last because it expects the blur
	// textures are already set up.
	gl_resize(gd, ps->root_width, ps->root_height);

	gd->logger = gl_string_marker_logger_new();
	if (gd->logger) {
		log_add_target_tls(gd->logger);
	}

	const char *vendor = (const char *)glGetString(GL_VENDOR);
	log_debug("GL_VENDOR = %s", vendor);
	if (strcmp(vendor, "NVIDIA Corporation") == 0) {
		log_info("GL vendor is NVIDIA, don't use glFinish");
		gd->is_nvidia = true;
	} else {
		gd->is_nvidia = false;
	}

	return true;
}

void gl_deinit(struct gl_data *gd) {
	gl_free_prog_main(&gd->win_shader);

	if (gd->logger) {
		log_remove_target_tls(gd->logger);
		gd->logger = NULL;
	}

	gl_check_err();
}

GLuint gl_new_texture(GLenum target) {
	GLuint texture;
	glGenTextures(1, &texture);
	if (!texture) {
		log_error("Failed to generate texture");
		return 0;
	}

	glBindTexture(target, texture);
	glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(target, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(target, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(target, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glBindTexture(target, 0);

	return texture;
}

/// Decouple `img` from the image it references, also applies all the lazy operations
static inline void gl_image_decouple(backend_t *base, struct gl_image *img) {
	if (img->inner->refcount == 1) {
		return;
	}

	struct gl_data *gl = (void *)base;
	auto new_tex = cmalloc(struct gl_texture);

	glGenTextures(1, &new_tex->texture);
	glBindTexture(GL_TEXTURE_2D, new_tex->texture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, img->inner->width, img->inner->height, 0,
	             GL_BGRA, GL_UNSIGNED_BYTE, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	new_tex->y_inverted = true;
	new_tex->height = img->inner->height;
	new_tex->width = img->inner->width;
	new_tex->refcount = 1;
	new_tex->user_data = gl->decouple_texture_user_data(base, img->inner->user_data);

	GLuint fbo;
	glGenFramebuffers(1, &fbo);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
	glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
	                       new_tex->texture, 0);
	glDrawBuffer(GL_COLOR_ATTACHMENT0);
	glClearColor(0, 0, 0, 0);
	glClear(GL_COLOR_BUFFER_BIT);

	// clang-format off
	GLfloat coord[] = {
		// top left
		0, 0,                 // vertex coord
		0, 0,                 // texture coord

		// top right
		(GLfloat)img->inner->width, 0, // vertex coord
		1, 0,                 // texture coord

		// bottom right
		(GLfloat)img->inner->width, (GLfloat)img->inner->height,
		1, 1,

		// bottom left
		0, (GLfloat)img->inner->height,
		0, 1
	};
	// clang-format on

	_gl_compose(base, img, fbo, coord, (GLuint[]){0, 1, 2, 2, 3, 0}, 1);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
	glDeleteFramebuffers(1, &fbo);

	img->inner->refcount--;
	img->inner = new_tex;

	// Clear lazy operation flags
	img->color_inverted = false;
	img->dim = 0;
	img->opacity = 1;
}

static void gl_image_apply_alpha(backend_t *base, struct gl_image *img,
                                 const region_t *reg_op, double alpha) {
	glBlendFunc(GL_ONE, GL_CONSTANT_COLOR);
	glBlendColor((GLclampf)alpha, (GLclampf)alpha, (GLclampf)alpha, (GLclampf)alpha);
	GLuint fbo;
	glGenFramebuffers(1, &fbo);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
	glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
	                       img->inner->texture, 0);
	glDrawBuffer(GL_COLOR_ATTACHMENT0);
	_gl_fill(base, (struct color){0, 0, 0, 0}, reg_op, 0, false);
	glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
	glDeleteFramebuffers(1, &fbo);
}

/// stub for backend_operations::image_op
bool gl_image_op(backend_t *base, enum image_operations op, void *image_data,
                 const region_t *reg_op, const region_t *reg_visible, void *arg) {
	struct gl_image *tex = image_data;
	int *iargs = arg;
	switch (op) {
	case IMAGE_OP_INVERT_COLOR_ALL: tex->color_inverted = true; break;
	case IMAGE_OP_DIM_ALL:
		tex->dim = 1.0 - (1.0 - tex->dim) * (1.0 - *(double *)arg);
		break;
	case IMAGE_OP_APPLY_ALPHA_ALL: tex->opacity *= *(double *)arg; break;
	case IMAGE_OP_APPLY_ALPHA:
		gl_image_decouple(base, tex);
		assert(tex->inner->refcount == 1);
		gl_image_apply_alpha(base, tex, reg_op, *(double *)arg);
		break;
	case IMAGE_OP_RESIZE_TILE:
		// texture is already set to repeat, so nothing else we need to do
		tex->ewidth = iargs[0];
		tex->eheight = iargs[1];
		break;
	}

	return true;
}

bool gl_is_image_transparent(backend_t *base, void *image_data) {
	struct gl_image *img = image_data;
	return img->has_alpha;
}