From 5b184a10a96663179ab8cb37b2875dd5b7a75922 Mon Sep 17 00:00:00 2001
From: Benjamin Otte <otte@redhat.com>
Date: Fri, 9 Feb 2024 02:55:33 +0100
Subject: [PATCH] gpu: Add a CLEAR blend mode for subsurface hole punching

The previous code was ignoring non-scissor clips, which would make it
overeager at punching holes.

It also was not working with fractional coordinates.

Fixes #6375
---
 gsk/gpu/gskgpublendop.c       |  6 ++++++
 gsk/gpu/gskgpunodeprocessor.c | 26 +++++++++++---------------
 gsk/gpu/gskgputypesprivate.h  |  3 ++-
 gsk/gpu/gskvulkandevice.c     | 15 ++++++++++++++-
 4 files changed, 33 insertions(+), 17 deletions(-)

diff --git a/gsk/gpu/gskgpublendop.c b/gsk/gpu/gskgpublendop.c
index b1ecc4a96e..53dd0f1f29 100644
--- a/gsk/gpu/gskgpublendop.c
+++ b/gsk/gpu/gskgpublendop.c
@@ -36,6 +36,9 @@ gsk_gpu_blend_op_print (GskGpuOp    *op,
       case GSK_GPU_BLEND_ADD:
         gsk_gpu_print_string (string, "add");
         break;
+      case GSK_GPU_BLEND_CLEAR:
+        gsk_gpu_print_string (string, "clear");
+        break;
       default:
         g_assert_not_reached ();
         break;
@@ -72,6 +75,9 @@ gsk_gpu_blend_op_gl_command (GskGpuOp          *op,
       case GSK_GPU_BLEND_ADD:
         glBlendFunc (GL_ONE, GL_ONE);
         break;
+      case GSK_GPU_BLEND_CLEAR:
+        glBlendFunc (GL_ZERO, GL_ONE_MINUS_SRC_ALPHA);
+        break;
       default:
         g_assert_not_reached ();
         break;
diff --git a/gsk/gpu/gskgpunodeprocessor.c b/gsk/gpu/gskgpunodeprocessor.c
index 1ac1efa36a..d522665c35 100644
--- a/gsk/gpu/gskgpunodeprocessor.c
+++ b/gsk/gpu/gskgpunodeprocessor.c
@@ -3674,22 +3674,18 @@ gsk_gpu_node_processor_add_subsurface_node (GskGpuNodeProcessor *self,
 
   if (!gdk_subsurface_is_above_parent (subsurface))
     {
-      cairo_rectangle_int_t int_rect;
+      self->blend = GSK_GPU_BLEND_CLEAR;
+      self->pending_globals |= GSK_GPU_GLOBAL_BLEND;
+      gsk_gpu_node_processor_sync_globals (self, 0);
 
-      if (!gsk_gpu_node_processor_rect_is_integer (self,
-                                                   &GRAPHENE_RECT_INIT (
-                                                     node->bounds.origin.x + self->offset.x,
-                                                     node->bounds.origin.y + self->offset.y,
-                                                     node->bounds.size.width,
-                                                     node->bounds.size.height
-                                                   ),
-                                                   &int_rect))
-        {
-          g_warning ("FIXME: non-integer aligned subsurface?!");
-        }
-      gsk_gpu_clear_op (self->frame,
-                        &int_rect,
-                        &GDK_RGBA_TRANSPARENT);
+      gsk_gpu_color_op (self->frame,
+                        gsk_gpu_clip_get_shader_clip (&self->clip, &self->offset, &node->bounds),
+                        &node->bounds,
+                        &self->offset,
+                        &GDK_RGBA_WHITE);
+
+      self->blend = GSK_GPU_BLEND_OVER;
+      self->pending_globals |= GSK_GPU_GLOBAL_BLEND;
     }
 }
 
diff --git a/gsk/gpu/gskgputypesprivate.h b/gsk/gpu/gskgputypesprivate.h
index 1ca780a217..a3f6c1d159 100644
--- a/gsk/gpu/gskgputypesprivate.h
+++ b/gsk/gpu/gskgputypesprivate.h
@@ -49,7 +49,8 @@ typedef enum {
 
 typedef enum {
   GSK_GPU_BLEND_OVER,
-  GSK_GPU_BLEND_ADD
+  GSK_GPU_BLEND_ADD,
+  GSK_GPU_BLEND_CLEAR
 } GskGpuBlend;
 
 typedef enum {
diff --git a/gsk/gpu/gskvulkandevice.c b/gsk/gpu/gskvulkandevice.c
index cc929f16e5..a542f937c2 100644
--- a/gsk/gpu/gskvulkandevice.c
+++ b/gsk/gpu/gskvulkandevice.c
@@ -892,7 +892,7 @@ struct _GskVulkanShaderSpecialization
   guint32 variation;
 };
 
-static VkPipelineColorBlendAttachmentState blend_attachment_states[2] = {
+static VkPipelineColorBlendAttachmentState blend_attachment_states[3] = {
   [GSK_GPU_BLEND_OVER] = {
     .blendEnable = VK_TRUE,
     .colorBlendOp = VK_BLEND_OP_ADD,
@@ -919,6 +919,19 @@ static VkPipelineColorBlendAttachmentState blend_attachment_states[2] = {
                     | VK_COLOR_COMPONENT_G_BIT
                     | VK_COLOR_COMPONENT_B_BIT
   },
+  [GSK_GPU_BLEND_CLEAR] = {
+    .blendEnable = VK_TRUE,
+    .colorBlendOp = VK_BLEND_OP_ADD,
+    .srcColorBlendFactor = VK_BLEND_FACTOR_ZERO,
+    .dstColorBlendFactor = VK_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA,
+    .alphaBlendOp = VK_BLEND_OP_ADD,
+    .srcAlphaBlendFactor = VK_BLEND_FACTOR_ZERO,
+    .dstAlphaBlendFactor = VK_BLEND_FACTOR_ONE_MINUS_SRC_ALPHA,
+    .colorWriteMask = VK_COLOR_COMPONENT_A_BIT
+                    | VK_COLOR_COMPONENT_R_BIT
+                    | VK_COLOR_COMPONENT_G_BIT
+                    | VK_COLOR_COMPONENT_B_BIT
+  },
 };
 
 VkPipeline