gsk: Introduce mask nodes

Add GskMaskNode, and support it in the render node
parser, in the inspector and in GtkSnapshot.

The rendering is just fallback for now.

Based on old work by Timm Bäder.

gsk/broadway/gskbroadwayrenderer.c

@@ -270,6 +270,7 @@ collect_reused_child_nodes (GskRenderer *renderer,
     case GSK_BLEND_NODE:
     case GSK_CROSS_FADE_NODE:
     case GSK_BLUR_NODE:
+    case GSK_MASK_NODE:
 
     default:
 
@@ -846,6 +847,7 @@ gsk_broadway_renderer_add_node (GskRenderer *renderer,
       }
       break; /* Fallback */
 
+    case GSK_MASK_NODE:
     case GSK_TEXTURE_SCALE_NODE:
     case GSK_TEXT_NODE:
     case GSK_RADIAL_GRADIENT_NODE:

gsk/gl/gskglrenderjob.c

@@ -3869,6 +3869,10 @@ gsk_gl_render_job_visit_node (GskGLRenderJob      *job,
         gsk_gl_render_job_visit_as_fallback (job, node);
     break;
 
+    case GSK_MASK_NODE:
+      gsk_gl_render_job_visit_as_fallback (job, node);
+    break;
+
     case GSK_OPACITY_NODE:
       gsk_gl_render_job_visit_opacity_node (job, node);
     break;

gsk/gskenums.h

@@ -46,6 +46,7 @@
  * @GSK_ROUNDED_CLIP_NODE: A node that clips its child to a rounded rectangle
  * @GSK_SHADOW_NODE: A node that draws a shadow below its child
  * @GSK_BLEND_NODE: A node that blends two children together
+ * @GSK_MASK_NODE: A node that masks one child with another
  * @GSK_CROSS_FADE_NODE: A node that cross-fades between two children
  * @GSK_TEXT_NODE: A node containing a glyph string
  * @GSK_BLUR_NODE: A node that applies a blur
@@ -77,6 +78,7 @@ typedef enum {
   GSK_ROUNDED_CLIP_NODE,
   GSK_SHADOW_NODE,
   GSK_BLEND_NODE,
+  GSK_MASK_NODE,
   GSK_CROSS_FADE_NODE,
   GSK_TEXT_NODE,
   GSK_BLUR_NODE,

gsk/gskrendernode.h

@@ -164,6 +164,7 @@ GskRenderNode *         gsk_render_node_deserialize             (GBytes
 #define GSK_TYPE_CROSS_FADE_NODE                (gsk_cross_fade_node_get_type())
 #define GSK_TYPE_TEXT_NODE                      (gsk_text_node_get_type())
 #define GSK_TYPE_BLUR_NODE                      (gsk_blur_node_get_type())
+#define GSK_TYPE_MASK_NODE                      (gsk_mask_node_get_type())
 #define GSK_TYPE_GL_SHADER_NODE                 (gsk_gl_shader_node_get_type())
 
 typedef struct _GskDebugNode                    GskDebugNode;
@@ -191,6 +192,7 @@ typedef struct _GskBlendNode                    GskBlendNode;
 typedef struct _GskCrossFadeNode                GskCrossFadeNode;
 typedef struct _GskTextNode                     GskTextNode;
 typedef struct _GskBlurNode                     GskBlurNode;
+typedef struct _GskMaskNode                     GskMaskNode;
 typedef struct _GskGLShaderNode                 GskGLShaderNode;
 
 GDK_AVAILABLE_IN_ALL
@@ -529,6 +531,16 @@ GskRenderNode *         gsk_blur_node_get_child                 (const GskRender
 GDK_AVAILABLE_IN_ALL
 float                   gsk_blur_node_get_radius                (const GskRenderNode      *node) G_GNUC_PURE;
 
+GDK_AVAILABLE_IN_4_10
+GType                  gsk_mask_node_get_type                   (void) G_GNUC_CONST;
+GDK_AVAILABLE_IN_4_10
+GskRenderNode *        gsk_mask_node_new                        (GskRenderNode            *source,
+                                                                 GskRenderNode            *mask);
+GDK_AVAILABLE_IN_4_10
+GskRenderNode *        gsk_mask_node_get_source                 (const GskRenderNode      *node);
+GDK_AVAILABLE_IN_4_10
+GskRenderNode *        gsk_mask_node_get_mask                   (const GskRenderNode      *node);
+
 GDK_AVAILABLE_IN_ALL
 GType                   gsk_gl_shader_node_get_type             (void) G_GNUC_CONST;
 GDK_AVAILABLE_IN_ALL

gsk/gskrendernodeimpl.c

@@ -5184,6 +5184,135 @@ gsk_blur_node_get_radius (const GskRenderNode *node)
   return self->radius;
 }
 
+/* }}} */
+/* {{{ GSK_MASK_NODE */
+
+/**
+ * GskMaskNode:
+ *
+ * A render node masking one child node with another.
+ *
+ * Since: 4.10
+ */
+typedef struct _GskMaskNode GskMaskNode;
+
+struct _GskMaskNode
+{
+  GskRenderNode render_node;
+
+  GskRenderNode *mask;
+  GskRenderNode *source;
+};
+
+static void
+gsk_mask_node_finalize (GskRenderNode *node)
+{
+  GskMaskNode *self = (GskMaskNode *) node;
+
+  gsk_render_node_unref (self->source);
+  gsk_render_node_unref (self->mask);
+}
+
+static void
+gsk_mask_node_draw (GskRenderNode *node,
+                    cairo_t       *cr)
+{
+  GskMaskNode *self = (GskMaskNode *) node;
+  cairo_pattern_t *mask_pattern;
+
+  cairo_push_group (cr);
+  gsk_render_node_draw (self->source, cr);
+  cairo_pop_group_to_source (cr);
+
+  cairo_push_group (cr);
+  gsk_render_node_draw (self->mask, cr);
+  mask_pattern = cairo_pop_group (cr);
+
+  cairo_mask (cr, mask_pattern);
+}
+
+static void
+gsk_mask_node_diff (GskRenderNode  *node1,
+                    GskRenderNode  *node2,
+                    cairo_region_t *region)
+{
+  GskMaskNode *self1 = (GskMaskNode *) node1;
+  GskMaskNode *self2 = (GskMaskNode *) node2;
+
+  gsk_render_node_diff (self1->source, self2->source, region);
+  gsk_render_node_diff (self1->mask, self2->mask, region);
+}
+
+/**
+ * gsk_mask_node_new:
+ * @source: The bottom node to be drawn
+ * @mask: The node to be blended onto the @bottom node
+ *
+ * Creates a `GskRenderNode` that will use @blend_mode to blend the @top
+ * node onto the @bottom node.
+ *
+ * Returns: (transfer full) (type GskMaskNode): A new `GskRenderNode`
+ *
+ * Since: 4.10
+ */
+GskRenderNode *
+gsk_mask_node_new (GskRenderNode *source,
+                   GskRenderNode *mask)
+{
+  GskMaskNode *self;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE (source), NULL);
+  g_return_val_if_fail (GSK_IS_RENDER_NODE (mask), NULL);
+
+  self = gsk_render_node_alloc (GSK_MASK_NODE);
+  self->source = gsk_render_node_ref (source);
+  self->mask = gsk_render_node_ref (mask);
+
+  graphene_rect_union (&source->bounds, &mask->bounds, &self->render_node.bounds);
+
+  return &self->render_node;
+}
+
+/**
+ * gsk_mask_node_get_source:
+ * @node: (type GskBlendNode): a mask `GskRenderNode`
+ *
+ * Retrieves the source `GskRenderNode` child of the @node.
+ *
+ * Returns: (transfer none): the source child node
+ *
+ * Since: 4.10
+ */
+GskRenderNode *
+gsk_mask_node_get_source (const GskRenderNode *node)
+{
+  const GskMaskNode *self = (const GskMaskNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_MASK_NODE), NULL);
+
+  return self->source;
+}
+
+/**
+ * gsk_mask_node_get_mask:
+ * @node: (type GskBlendNode): a mask `GskRenderNode`
+ *
+ * Retrieves the mask `GskRenderNode` child of the @node.
+ *
+ * Returns: (transfer none): the mask child node
+ *
+ * Since: 4.10
+ */
+GskRenderNode *
+gsk_mask_node_get_mask (const GskRenderNode *node)
+{
+  const GskMaskNode *self = (const GskMaskNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_MASK_NODE), NULL);
+
+  return self->mask;
+}
+
 /* }}} */
 /* {{{ GSK_DEBUG_NODE */
 
@@ -5556,6 +5685,7 @@ GSK_DEFINE_RENDER_NODE_TYPE (gsk_blend_node, GSK_BLEND_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_cross_fade_node, GSK_CROSS_FADE_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_text_node, GSK_TEXT_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_blur_node, GSK_BLUR_NODE)
+GSK_DEFINE_RENDER_NODE_TYPE (gsk_mask_node, GSK_MASK_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_gl_shader_node, GSK_GL_SHADER_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_debug_node, GSK_DEBUG_NODE)
 
@@ -5946,6 +6076,22 @@ gsk_render_node_init_types_once (void)
     gsk_render_node_types[GSK_BLUR_NODE] = node_type;
   }
 
+  {
+    const GskRenderNodeTypeInfo node_info =
+    {
+      GSK_MASK_NODE,
+      sizeof (GskMaskNode),
+      NULL,
+      gsk_mask_node_finalize,
+      gsk_mask_node_draw,
+      NULL,
+      gsk_mask_node_diff,
+    };
+
+    GType node_type = gsk_render_node_type_register_static (I_("GskMaskNode"), &node_info);
+    gsk_render_node_types[GSK_MASK_NODE] = node_type;
+  }
+
   {
     const GskRenderNodeTypeInfo node_info =
     {

gsk/gskrendernodeparser.c

@@ -1376,6 +1376,31 @@ parse_glshader_node (GtkCssParser *parser)
   return node;
 }
 
+static GskRenderNode *
+parse_mask_node (GtkCssParser *parser)
+{
+  GskRenderNode *source = NULL;
+  GskRenderNode *mask = NULL;
+  const Declaration declarations[] = {
+    { "source", parse_node, clear_node, &source },
+    { "mask", parse_node, clear_node, &mask },
+  };
+  GskRenderNode *result;
+
+  parse_declarations (parser, declarations, G_N_ELEMENTS(declarations));
+  if (source == NULL)
+    source = create_default_render_node ();
+  if (mask == NULL)
+    mask = gsk_color_node_new (&GDK_RGBA("AAFF00"), &GRAPHENE_RECT_INIT (0, 0, 50, 50));
+
+  result = gsk_mask_node_new (source, mask);
+
+  gsk_render_node_unref (source);
+  gsk_render_node_unref (mask);
+
+  return result;
+}
+
 static GskRenderNode *
 parse_border_node (GtkCssParser *parser)
 {
@@ -1914,6 +1939,7 @@ parse_node (GtkCssParser *parser,
     { "texture-scale", parse_texture_scale_node },
     { "transform", parse_transform_node },
     { "glshader", parse_glshader_node },
+    { "mask", parse_mask_node },
   };
   GskRenderNode **node_p = out_node;
   guint i;
@@ -3100,6 +3126,17 @@ render_node_print (Printer       *p,
       }
       break;
 
+    case GSK_MASK_NODE:
+      {
+        start_node (p, "mask");
+
+        append_node_param (p, "source", gsk_mask_node_get_source (node));
+        append_node_param (p, "mask", gsk_mask_node_get_mask (node));
+
+        end_node (p);
+      }
+      break;
+
     case GSK_NOT_A_RENDER_NODE:
       g_assert_not_reached ();
       break;

gsk/vulkan/gskvulkanrenderpass.c

@@ -504,6 +504,9 @@ gsk_vulkan_render_pass_add_node (GskVulkanRenderPass           *self,
       g_array_append_val (self->render_ops, op);
       return;
 
+    case GSK_MASK_NODE:
+      goto fallback;
+
     case GSK_COLOR_MATRIX_NODE:
       if (gsk_vulkan_clip_contains_rect (&constants->clip, &node->bounds))
         pipeline_type = GSK_VULKAN_PIPELINE_COLOR_MATRIX;

gtk/inspector/recorder.c

@@ -305,6 +305,10 @@ create_list_model_for_render_node (GskRenderNode *node)
       return create_render_node_list_model ((GskRenderNode *[2]) { gsk_blend_node_get_bottom_child (node),
                                                                    gsk_blend_node_get_top_child (node) }, 2);
 
+    case GSK_MASK_NODE:
+      return create_render_node_list_model ((GskRenderNode *[2]) { gsk_mask_node_get_source (node),
+                                                                   gsk_mask_node_get_mask (node) }, 2);
+
     case GSK_CROSS_FADE_NODE:
       return create_render_node_list_model ((GskRenderNode *[2]) { gsk_cross_fade_node_get_start_child (node),
                                                                    gsk_cross_fade_node_get_end_child (node) }, 2);
@@ -425,6 +429,8 @@ node_type_name (GskRenderNodeType type)
       return "Shadow";
     case GSK_BLEND_NODE:
       return "Blend";
+    case GSK_MASK_NODE:
+      return "Mask";
     case GSK_CROSS_FADE_NODE:
       return "CrossFade";
     case GSK_TEXT_NODE:
@@ -462,6 +468,7 @@ node_name (GskRenderNode *node)
     case GSK_ROUNDED_CLIP_NODE:
     case GSK_SHADOW_NODE:
     case GSK_BLEND_NODE:
+    case GSK_MASK_NODE:
     case GSK_CROSS_FADE_NODE:
     case GSK_TEXT_NODE:
     case GSK_BLUR_NODE:
@@ -1132,6 +1139,9 @@ populate_render_node_properties (GListStore    *store,
       }
       break;
 
+    case GSK_MASK_NODE:
+      break;
+
     case GSK_BLUR_NODE:
       add_float_row (store, "Radius", gsk_blur_node_get_radius (node));
       break;