renderer/layout: add a shadow_opacity per layer property

Prepare for making shadow opacity animatable. Also fix the fact that
shadows aren't been rendered with the correct opacity currently.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/picom.c

@@ -1012,9 +1012,6 @@ static bool paint_preprocess(session_t *ps, bool *fade_running, bool *animation,
 		log_trace("|- will be painted");
 		log_verbose("Window %#010x (%s) will be painted", w->base.id, w->name);
 
-		// Calculate shadow opacity
-		w->shadow_opacity = ps->o.shadow_opacity * window_opacity * ps->o.frame_opacity;
-
 		// Generate ignore region for painting to reduce GPU load
 		if (!w->reg_ignore) {
 			w->reg_ignore = rc_region_ref(last_reg_ignore);

src/render.c

@@ -808,8 +808,10 @@ win_paint_shadow(session_t *ps, struct managed_win *w, region_t *reg_paint) {
 	    .x = -(w->shadow_dx),
 	    .y = -(w->shadow_dy),
 	};
+	double shadow_opacity =
+	    animatable_get(&w->opacity) * ps->o.shadow_opacity * ps->o.frame_opacity;
 	render(ps, 0, 0, w->g.x + w->shadow_dx, w->g.y + w->shadow_dy, w->shadow_width,
-	       w->shadow_height, w->widthb, w->heightb, w->shadow_opacity, true, false, 0,
+	       w->shadow_height, w->widthb, w->heightb, shadow_opacity, true, false, 0,
 	       w->shadow_paint.pict, w->shadow_paint.ptex, reg_paint, NULL,
 	       should_clip ? &clip : NULL);
 	if (td) {

src/renderer/command_builder.c

@@ -155,7 +155,7 @@ command_for_shadow(struct layer *layer, struct backend_command *cmd,
 	}
 	log_region(TRACE, &cmd->mask.region);
 	cmd->blit = (struct backend_blit_args){
-	    .opacity = layer->opacity,
+	    .opacity = layer->shadow_opacity,
 	    .max_brightness = 1,
 	    .mask = &cmd->mask,
 	    .effective_size = layer->shadow_size,

src/renderer/layout.c

@@ -64,6 +64,8 @@ static bool layer_from_window(struct layer *out_layer, struct managed_win *w, iv
 
 	out_layer->opacity = (float)animatable_get(&w->opacity);
 	out_layer->blur_opacity = (float)animatable_get(&w->blur_opacity);
+	out_layer->shadow_opacity =
+	    (float)(out_layer->opacity * w->shadow_opacity * w->frame_opacity);
 	if (out_layer->opacity == 0 && out_layer->blur_opacity == 0) {
 		goto out;
 	}

src/renderer/layout.h

@@ -41,6 +41,8 @@ struct layer {
 	float opacity;
 	/// Opacity of the background blur of this window
 	float blur_opacity;
+	/// Opacity of this window's shadow
+	float shadow_opacity;
 
 	/// How many commands are needed to render this layer
 	unsigned number_of_commands;

src/win.c

@@ -1590,7 +1590,6 @@ struct win *attr_ret_nonnull maybe_allocate_managed_win(session_t *ps, struct wi
 	    // No need to initialize. (or, you can think that
 	    // they are initialized right here).
 	    // The following ones are updated during paint or paint preprocess
-	    .shadow_opacity = 0.0,
 	    .to_paint = false,
 	    .frame_opacity = 1.0,
 	    .dim = false,
@@ -1727,6 +1726,7 @@ struct win *attr_ret_nonnull maybe_allocate_managed_win(session_t *ps, struct wi
 	new->a = *a;
 	new->opacity = animatable_new(0);
 	new->blur_opacity = animatable_new(0);
+	new->shadow_opacity = ps->o.shadow_opacity;
 	pixman_region32_init(&new->bounding_shape);
 
 	free(a);

src/win.h

@@ -253,7 +253,8 @@ struct managed_win {
 	bool shadow;
 	/// Override value of window shadow state. Set by D-Bus method calls.
 	switch_t shadow_force;
-	/// Opacity of the shadow. Affected by window opacity and frame opacity.
+	/// Window specific shadow factor. The final shadow opacity is a combination of
+	/// this, the window opacity, and the window frame opacity.
 	double shadow_opacity;
 	/// X offset of shadow. Affected by command line argument.
 	int shadow_dx;