windowManager: Use an off-screen buffer for window dimming

The way the window dimmer shader is applied will cause rendering errors with
the rounded corners, invisible borders or shaped textures since it doesn't deal
well with the multitexturing used by the MetaShapedTexture. Use an off-screen
buffer to flatten the texture before being applied.

https://bugzilla.gnome.org/show_bug.cgi?id=659302

data/shaders/dim-window.glsl

@@ -1,5 +1,5 @@
 #version 110
-uniform sampler2D sampler0;
+uniform sampler2D tex;
 uniform float fraction;
 uniform float height;
 const float c = -0.2;
@@ -12,15 +12,17 @@ mat4 contrast = mat4 (1.0 + c, 0.0, 0.0, 0.0,
 vec4 off = vec4(0.633, 0.633, 0.633, 0);
 void main()
 {
-  vec4 color = texture2D(sampler0, gl_TexCoord[0].st);
-  float y = height * gl_TexCoord[0][1];
+  vec4 color = texture2D(tex, cogl_tex_coord_in[0].xy);
+  float y = height * cogl_tex_coord_in[0].y;
 
   // To reduce contrast, blend with a mid gray
-  gl_FragColor = color * contrast - off * c;
+  cogl_color_out = color * contrast - off * c;
 
   // We only fully dim at a distance of BORDER_MAX_HEIGHT from the edge and
   // when the fraction is 1.0. For other locations and fractions we linearly
   // interpolate back to the original undimmed color.
-  gl_FragColor = color + (gl_FragColor - color) * min(y / border_max_height, 1.0);
-  gl_FragColor = color + (gl_FragColor - color) * fraction;
+  cogl_color_out = color + (cogl_color_out - color) * min(y / border_max_height, 1.0);
+  cogl_color_out = color + (cogl_color_out - color) * fraction;
+
+  cogl_color_out *= color.a;
 }

js/ui/windowManager.js

@@ -19,22 +19,9 @@ const UNDIM_TIME = 0.250;
 
 var dimShader = undefined;
 
-function getDimShader() {
-    if (dimShader === null)
-        return null;
-    if (!dimShader) {
-        let source = Shell.get_file_contents_utf8_sync(global.datadir + '/shaders/dim-window.glsl');
-        try {
-            let shader = new Clutter.Shader();
-            shader.set_fragment_source(source, -1);
-            shader.compile();
-
-            dimShader = shader;
-        } catch (e) {
-            log(e.message);
-            dimShader = null;
-        }
-    }
+function getDimShaderSource() {
+    if (!dimShader)
+        dimShader = Shell.get_file_contents_utf8_sync(global.datadir + '/shaders/dim-window.glsl');
     return dimShader;
 }
 
@@ -44,22 +31,29 @@ function WindowDimmer(actor) {
 
 WindowDimmer.prototype = {
     _init: function(actor) {
+        this.effect = new Clutter.ShaderEffect({ shader_type: Clutter.ShaderType.FRAGMENT_SHADER });
+        this.effect.set_shader_source(getDimShaderSource());
+
         this.actor = actor;
     },
 
     set dimFraction(fraction) {
         this._dimFraction = fraction;
-        let shader = getDimShader();
-        if (!Meta.prefs_get_attach_modal_dialogs() || !shader) {
-            this.actor.set_shader(null);
+        if (!Meta.prefs_get_attach_modal_dialogs()) {
+            this.effect.enabled = false;
             return;
         }
+
         if (fraction > 0.01) {
-            this.actor.set_shader(shader);
-            this.actor.set_shader_param_float('height', this.actor.get_height());
-            this.actor.set_shader_param_float('fraction', fraction);
-        } else
-            this.actor.set_shader(null);
+            Shell.shader_effect_set_double_uniform(this.effect, 'height', this.actor.get_height());
+            Shell.shader_effect_set_double_uniform(this.effect, 'fraction', fraction);
+
+            if (!this.effect.actor)
+                this.actor.add_effect(this.effect);
+        } else {
+            if (this.effect.actor)
+                this.actor.remove_effect(this.effect);
+        }
     },
 
     get dimFraction() {

src/shell-util.c

@@ -850,3 +850,31 @@ shell_parse_search_provider (const char    *data,
 
   return FALSE;
 }
+
+/**
+ * shell_shader_effect_set_double_uniform:
+ * @effect: The #ClutterShaderEffect
+ * @name: The name of the uniform
+ * @value: The value to set it to.
+ *
+ * Set a double uniform on a ClutterShaderEffect.
+ *
+ * The problem here is that JavaScript doesn't have more than
+ * one number type, and gjs tries to automatically guess what
+ * type we want to set a GValue to. If the number is "1.0" or
+ * something, it will use an integer, which will cause errors
+ * in GLSL.
+ */
+void
+shell_shader_effect_set_double_uniform (ClutterShaderEffect *effect,
+                                        const gchar         *name,
+                                        gdouble             value)
+{
+  GValue gvalue = G_VALUE_INIT;
+  g_value_init (&gvalue, G_TYPE_DOUBLE);
+  g_value_set_double (&gvalue, value);
+
+  clutter_shader_effect_set_uniform_value (effect,
+                                           name,
+                                           &gvalue);
+}

src/shell-util.h

@@ -50,6 +50,10 @@ gboolean shell_parse_search_provider           (const char       *data,
                                                 char            **icon_data_uri,
                                                 GError          **error);
 
+void shell_shader_effect_set_double_uniform (ClutterShaderEffect *effect,
+                                             const gchar         *name,
+                                             gdouble             value);
+
 G_END_DECLS
 
 #endif /* __SHELL_UTIL_H__ */