backend: gl: do not use larger-than-screen textures for blur buffers

Blur-texture sampling has been changed to `CLAMP_TO_EDGE` in commit
4b0ff37b36 and to using the buffer
textures at screen position instead of texture origin in commit
89c18afac6.

When using the above approach, expanding the buffer textures by the same
amount as the damage region is not needed anymore, as we cannot render
more than the screen region anyways. Having larger-than-screen buffer
textures might lead to a slight darkening at the upper and right edges
since we don't necessarily trigger the `CLAMP_TO_EDGE` condition in the
intermediate steps. This becomes apparent when using dual-kawase at large
blur-strengths with light backgrounds.

These changes do not affect the general approach of rendering a
larger-than-window region with the blur to accommodate the necessary
increase in damage region.

Related: 6d646b543f

src/backend/gl/gl_common.c

@@ -556,8 +556,7 @@ bool gl_kernel_blur(backend_t *base, double opacity, void *ctx, const rect_t *ex
 	auto bctx = (struct gl_blur_context *)ctx;
 	auto gd = (struct gl_data *)base;
 
-	int dst_y_screen_coord = gd->height - extent->y2,
+	int dst_y_fb_coord = bctx->fb_height - extent->y2;
-	    dst_y_fb_coord = bctx->fb_height - extent->y2;
 
 	int curr = 0;
 	for (int i = 0; i < bctx->npasses; ++i) {
@@ -567,19 +566,15 @@ bool gl_kernel_blur(backend_t *base, double opacity, void *ctx, const rect_t *ex
 		assert(bctx->blur_textures[curr]);
 
 		// The origin to use when sampling from the source texture
-		GLint texorig_x, texorig_y;
+		GLint texorig_x = extent->x1, texorig_y = dst_y_fb_coord;
 		GLint tex_width, tex_height;
 		GLuint src_texture;
 
 		if (i == 0) {
-			texorig_x = extent->x1;
-			texorig_y = dst_y_screen_coord;
 			src_texture = gd->back_texture;
 			tex_width = gd->width;
 			tex_height = gd->height;
 		} else {
-			texorig_x = extent->x1 + bctx->resize_width;
-			texorig_y = dst_y_fb_coord - bctx->resize_height;
 			src_texture = bctx->blur_textures[curr];
 			auto src_size = bctx->texture_sizes[curr];
 			tex_width = src_size.width;
@@ -611,8 +606,6 @@ bool gl_kernel_blur(backend_t *base, double opacity, void *ctx, const rect_t *ex
 			}
 
 			glUniform1f(p->unifm_opacity, 1.0);
-			glUniform2f(p->orig_loc, (GLfloat)bctx->resize_width,
-			            -(GLfloat)bctx->resize_height);
 		} else {
 			// last pass, draw directly into the back buffer, with origin
 			// regions
@@ -621,7 +614,6 @@ bool gl_kernel_blur(backend_t *base, double opacity, void *ctx, const rect_t *ex
 			glBindFramebuffer(GL_FRAMEBUFFER, gd->back_fbo);
 
 			glUniform1f(p->unifm_opacity, (float)opacity);
-			glUniform2f(p->orig_loc, 0, 0);
 		}
 
 		glUniform2f(p->texorig_loc, (GLfloat)texorig_x, (GLfloat)texorig_y);
@@ -641,8 +633,7 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 	auto bctx = (struct gl_blur_context *)ctx;
 	auto gd = (struct gl_data *)base;
 
-	int dst_y_screen_coord = gd->height - extent->y2,
+	int dst_y_fb_coord = bctx->fb_height - extent->y2;
-	    dst_y_fb_coord = bctx->fb_height - extent->y2;
 
 	int iterations = bctx->blur_texture_count;
 	int scale_factor = 1;
@@ -652,9 +643,7 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 	assert(down_pass->prog);
 	glUseProgram(down_pass->prog);
 
-	// Downsample always renders with resize offset
+	glUniform2f(down_pass->texorig_loc, (GLfloat)extent->x1, (GLfloat)dst_y_fb_coord);
-	glUniform2f(down_pass->orig_loc, (GLfloat)bctx->resize_width,
-	            -(GLfloat)bctx->resize_height);
 
 	for (int i = 0; i < iterations; ++i) {
 		// Scale output width / height by half in each iteration
@@ -662,25 +651,18 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 
 		GLuint src_texture;
 		int tex_width, tex_height;
-		int texorig_x, texorig_y;
 
 		if (i == 0) {
 			// first pass: copy from back buffer
 			src_texture = gd->back_texture;
 			tex_width = gd->width;
 			tex_height = gd->height;
-
-			texorig_x = extent->x1;
-			texorig_y = dst_y_screen_coord;
 		} else {
 			// copy from previous pass
 			src_texture = bctx->blur_textures[i - 1];
 			auto src_size = bctx->texture_sizes[i - 1];
 			tex_width = src_size.width;
 			tex_height = src_size.height;
-
-			texorig_x = extent->x1 + bctx->resize_width;
-			texorig_y = dst_y_fb_coord - bctx->resize_height;
 		}
 
 		assert(src_texture);
@@ -692,7 +674,6 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, bctx->blur_fbos[i]);
 		glDrawBuffer(GL_COLOR_ATTACHMENT0);
 
-		glUniform2f(down_pass->texorig_loc, (GLfloat)texorig_x, (GLfloat)texorig_y);
 		glUniform1f(down_pass->scale_loc, (GLfloat)scale_factor);
 
 		glUniform2f(down_pass->unifm_pixel_norm, 1.0f / (GLfloat)tex_width,
@@ -706,9 +687,7 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 	assert(up_pass->prog);
 	glUseProgram(up_pass->prog);
 
-	// Upsample always samples from textures with resize offset
+	glUniform2f(up_pass->texorig_loc, (GLfloat)extent->x1, (GLfloat)dst_y_fb_coord);
-	glUniform2f(up_pass->texorig_loc, (GLfloat)(extent->x1 + bctx->resize_width),
-	            (GLfloat)(dst_y_fb_coord - bctx->resize_height));
 
 	for (int i = iterations - 1; i >= 0; --i) {
 		// Scale output width / height back by two in each iteration
@@ -735,8 +714,6 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 			glBindFramebuffer(GL_DRAW_FRAMEBUFFER, bctx->blur_fbos[i - 1]);
 			glDrawBuffer(GL_COLOR_ATTACHMENT0);
 
-			glUniform2f(up_pass->orig_loc, (GLfloat)bctx->resize_width,
-			            -(GLfloat)bctx->resize_height);
 			glUniform1f(up_pass->unifm_opacity, (GLfloat)1);
 		} else {
 			// last pass, draw directly into the back buffer
@@ -744,7 +721,6 @@ bool gl_dual_kawase_blur(backend_t *base, double opacity, void *ctx, const rect_
 			nelems = vao_nelems[0];
 			glBindFramebuffer(GL_FRAMEBUFFER, gd->back_fbo);
 
-			glUniform2f(up_pass->orig_loc, (GLfloat)0, (GLfloat)0);
 			glUniform1f(up_pass->unifm_opacity, (GLfloat)opacity);
 		}
 
@@ -765,12 +741,11 @@ bool gl_blur(backend_t *base, double opacity, void *ctx, const region_t *reg_blu
 
 	bool ret = false;
 
-	if (gd->width + bctx->resize_width * 2 != bctx->fb_width ||
+	if (gd->width != bctx->fb_width || gd->height != bctx->fb_height) {
-	    gd->height + bctx->resize_height * 2 != bctx->fb_height) {
 		// Resize the temporary textures used for blur in case the root
 		// size changed
-		bctx->fb_width = gd->width + bctx->resize_width * 2;
+		bctx->fb_width = gd->width;
-		bctx->fb_height = gd->height + bctx->resize_height * 2;
+		bctx->fb_height = gd->height;
 
 		for (int i = 0; i < bctx->blur_texture_count; ++i) {
 			auto tex_size = bctx->texture_sizes + i;
@@ -894,13 +869,12 @@ bool gl_blur(backend_t *base, double opacity, void *ctx, const region_t *reg_blu
 const char *vertex_shader = GLSL(330,
 	uniform mat4 projection;
 	uniform float scale = 1.0;
-	uniform vec2 orig;
 	uniform vec2 texorig;
 	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, scale);
+		gl_Position = projection * vec4(coord, 0, scale);
 		texcoord = in_texcoord + texorig;
 	}
 );
@@ -927,10 +901,6 @@ static int gl_win_shader_from_string(const char *vshader_str, const char *fshade
 	ret->unifm_max_brightness =
 	    glGetUniformLocationChecked(ret->prog, "max_brightness");
 
-	glUseProgram(ret->prog);
-	int orig_loc = glGetUniformLocation(ret->prog, "orig");
-	glUniform2f(orig_loc, 0, 0);
-
 	gl_check_err();
 
 	return true;
@@ -1279,7 +1249,6 @@ bool gl_create_kernel_blur_context(void *blur_context, GLfloat *projection,
 		pass->unifm_pixel_norm =
 		    glGetUniformLocationChecked(pass->prog, "pixel_norm");
 		pass->unifm_opacity = glGetUniformLocationChecked(pass->prog, "opacity");
-		pass->orig_loc = glGetUniformLocationChecked(pass->prog, "orig");
 		pass->texorig_loc = glGetUniformLocationChecked(pass->prog, "texorig");
 
 		// Setup projection matrix
@@ -1299,7 +1268,6 @@ bool gl_create_kernel_blur_context(void *blur_context, GLfloat *projection,
 		pass->prog = gl_create_program_from_str(vertex_shader, dummy_frag);
 		pass->unifm_pixel_norm = -1;
 		pass->unifm_opacity = -1;
-		pass->orig_loc = glGetUniformLocationChecked(pass->prog, "orig");
 		pass->texorig_loc = glGetUniformLocationChecked(pass->prog, "texorig");
 
 		// Setup projection matrix
@@ -1400,8 +1368,6 @@ bool gl_create_dual_kawase_blur_context(void *blur_context, GLfloat *projection,
 		// Get uniform addresses
 		down_pass->unifm_pixel_norm =
 		    glGetUniformLocationChecked(down_pass->prog, "pixel_norm");
-		down_pass->orig_loc =
-		    glGetUniformLocationChecked(down_pass->prog, "orig");
 		down_pass->texorig_loc =
 		    glGetUniformLocationChecked(down_pass->prog, "texorig");
 		down_pass->scale_loc =
@@ -1465,7 +1431,6 @@ bool gl_create_dual_kawase_blur_context(void *blur_context, GLfloat *projection,
 		    glGetUniformLocationChecked(up_pass->prog, "pixel_norm");
 		up_pass->unifm_opacity =
 		    glGetUniformLocationChecked(up_pass->prog, "opacity");
-		up_pass->orig_loc = glGetUniformLocationChecked(up_pass->prog, "orig");
 		up_pass->texorig_loc =
 		    glGetUniformLocationChecked(up_pass->prog, "texorig");
 		up_pass->scale_loc = glGetUniformLocationChecked(up_pass->prog, "scale");

src/backend/gl/gl_common.h

@@ -34,7 +34,6 @@ typedef struct {
 	GLuint prog;
 	GLint unifm_pixel_norm;
 	GLint unifm_opacity;
-	GLint orig_loc;
 	GLint texorig_loc;
 	GLint scale_loc;
 } gl_blur_shader_t;