compositor: Add opaque rect shader feature

This lets us mark a rectangle in a texture and force the alpha to one
inside.  This is useful for textures coming from X windows, where the X
window part is xRGB, that is 32 bit RGB with an undefined alpha channel
and the decorations are rendered with a well-defined alpha channel.

src/compositor.c

@@ -228,6 +228,10 @@ weston_surface_create(struct weston_compositor *compositor)
 	surface->alpha = 255;
 	surface->brightness = 255;
 	surface->saturation = 255;
+	surface->opaque_rect[0] = 0.0;
+	surface->opaque_rect[1] = 0.0;
+	surface->opaque_rect[2] = 0.0;
+	surface->opaque_rect[3] = 0.0;
 	surface->pitch = 1;
 
 	surface->buffer = NULL;
@@ -861,6 +865,7 @@ weston_surface_draw(struct weston_surface *es, struct weston_output *output,
 	glUniform1f(es->shader->saturation_uniform, es->saturation / 255.0);
 	glUniform1f(es->shader->texwidth_uniform,
 		    (GLfloat)es->geometry.width / es->pitch);
+	glUniform4fv(es->shader->opaque_uniform, 1, es->opaque_rect);
 
 	if (es->transform.enabled || output->zoom.active)
 		filter = GL_LINEAR;
@@ -2325,6 +2330,7 @@ static const char texture_fragment_shader[] =
 	"uniform float bright;\n"
 	"uniform float saturation;\n"
 	"uniform float texwidth;\n"
+	"uniform vec4 opaque;\n"
 	"void main()\n"
 	"{\n"
 	"   if (v_texcoord.x < 0.0 || v_texcoord.x > texwidth ||\n"
@@ -2335,6 +2341,9 @@ static const char texture_fragment_shader[] =
 	"   vec3 range = (gl_FragColor.rgb - vec3 (gray, gray, gray)) * saturation;\n"
 	"   gl_FragColor = vec4(vec3(gray + range), gl_FragColor.a);\n"
 	"   gl_FragColor = vec4(vec3(bright, bright, bright) * gl_FragColor.rgb, gl_FragColor.a);\n"
+	"   if (opaque.x <= v_texcoord.x && v_texcoord.x < opaque.y &&\n"
+	"       opaque.z <= v_texcoord.y && v_texcoord.y < opaque.w)\n"
+	"      gl_FragColor.a = 1.0;\n"
 	"   gl_FragColor = alpha * gl_FragColor;\n"
 	"}\n";
 
@@ -2401,6 +2410,8 @@ weston_shader_init(struct weston_shader *shader,
 	shader->color_uniform = glGetUniformLocation(shader->program, "color");
 	shader->texwidth_uniform = glGetUniformLocation(shader->program,
 							"texwidth");
+	shader->opaque_uniform =
+		glGetUniformLocation(shader->program, "opaque");
 
 	return 0;
 }

src/compositor.h

@@ -166,6 +166,7 @@ struct weston_shader {
 	GLint saturation_uniform;
 	GLint color_uniform;
 	GLint texwidth_uniform;
+	GLint opaque_uniform;
 };
 
 struct weston_animation {
@@ -326,6 +327,7 @@ struct weston_surface {
 	struct wl_list layer_link;
 	struct weston_shader *shader;
 	GLfloat color[4];
+	GLfloat opaque_rect[4];
 	uint32_t alpha;
 	uint32_t brightness;
 	uint32_t saturation;

src/xserver-launcher.c

@@ -841,6 +841,22 @@ weston_wm_window_draw_decoration(void *data)
 
 	cairo_destroy(cr);
 	cairo_surface_destroy(surface);
+
+	if (window->surface) {
+		/* We leave an extra pixel around the X window area to
+		 * make sure we don't sample from the undefined alpha
+		 * channel when filtering. */
+		window->surface->opaque_rect[0] =
+			(double) (t->margin + t->width - 1) / width;
+		window->surface->opaque_rect[1] =
+			(double) (t->margin + t->width + 
+				  window->width + 1) / width;
+		window->surface->opaque_rect[2] =
+			(double) (t->margin + t->titlebar_height - 1) / height;
+		window->surface->opaque_rect[3] =
+			(double) (t->margin + t->titlebar_height +
+				  window->height + 1) / height;
+	}
 }
 
 static void
@@ -1767,6 +1783,8 @@ xserver_set_window_id(struct wl_client *client, struct wl_resource *resource,
 	wl_signal_add(&surface->resource.destroy_signal,
 		      &window->surface_destroy_listener);
 
+	weston_wm_window_schedule_repaint(window);
+
 	if (shell_interface->create_shell_surface) {
 		shell_interface->create_shell_surface(shell_interface->shell,
 						      window->surface,