From 7e6cd36d2619539ca63416d2673434fe5c4fd0dc Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 27 Jul 2026 23:11:43 +0530
Subject: [PATCH] Wire up the backbuffer sampler

---
 kitty/shaders/custom/pipeline.slang | 56 ++++++++++++++++++-----------
 kitty/shaders/custom/types.slang    |  3 +-
 kitty/shaders/slang.py              |  2 +-
 3 files changed, 39 insertions(+), 22 deletions(-)

diff --git a/kitty/shaders/custom/pipeline.slang b/kitty/shaders/custom/pipeline.slang
index 0fb0092e8..2582764b7 100644
--- a/kitty/shaders/custom/pipeline.slang
+++ b/kitty/shaders/custom/pipeline.slang
@@ -4,37 +4,53 @@
 
 // IMPORTS
 
-static const int LEFT = 0;
-static const int TOP = 1;
-static const int RIGHT = 2;
-static const int BOTTOM = 3;
-static const uint FF = 0xff;
-
-static const uint2 pos_map[4] = {
-    uint2(RIGHT, TOP),
-    uint2(RIGHT, BOTTOM),
-    uint2(LEFT, BOTTOM),
-    uint2(LEFT, TOP)
+public struct BlitOutput {
+    public float2 texcoord;
+    public float2 position;
 };
 
+#define left 0
+#define top 1
+#define right 2
+#define bottom 3
+
+// Static constant array mapping vertex IDs
+static const int2 vertex_pos_map[4] = {
+    {right, top},
+    {right, bottom},
+    {left, bottom},
+    {left, top}
+};
+
+public BlitOutput get_coords_for_blit(uint vertex_id, float4 src_rect, float4 dest_rect) {
+    int2 pos = vertex_pos_map[vertex_id];
+    BlitOutput output;
+    output.texcoord = float2(src_rect[pos.x], src_rect[pos.y]);
+    output.position = float2(dest_rect[pos.x], dest_rect[pos.y]);
+    return output;
+}
+
 struct VertexOutput {
+    float2 texcoord : TEXCOORD;
     float4 position : SV_Position;
-    KittyCustomShaderData d;
 };
 
 
 [shader("vertex")]
-VertexOutput vertex_main(float4 rect, uint vertex_id : SV_VertexID) {
-    uint2 pos = pos_map[vertex_id];
-    VertexOutput vo;
-    vo.position = float4(rect[pos.x], rect[pos.y], 0, 1);
-    return vo;
+VertexOutput vertex_main(float4 src_rect, float4 dest_rect, uint vertex_id : SV_VertexID) {
+    BlitOutput ans = get_coords_for_blit(vertex_id, src_rect, dest_rect);
+    return {ans.texcoord, float4(ans.position[0], ans.position[1], 0.0, 1.0)};
 }
 
+uniform Sampler2D backbuffer;
+
 [shader("fragment")]
-float4 pipeline_fragment_main(VertexOutput vo) : SV_Target {
-    vo.d.pos = vo.position;
-    float4 color = float4(1, 1, 1, 1);  // TODO: load from framebuffer
+float4 pipeline_fragment_main(float2 texcoord : TEXCOORD) : SV_Target {
+    KittyCustomShaderData d;
+    d.backbuffer = backbuffer;
+    d.texcoord = texcoord;
+    d.backbuffer = backbuffer;
+    float4 color = backbuffer.Sample(texcoord);
     // PIPELINE
     return color;
 }
diff --git a/kitty/shaders/custom/types.slang b/kitty/shaders/custom/types.slang
index 4b7f236a3..c5d0c5a5f 100644
--- a/kitty/shaders/custom/types.slang
+++ b/kitty/shaders/custom/types.slang
@@ -6,5 +6,6 @@
 
 public struct KittyCustomShaderData {
     public uint timestamp;
-    public float4 pos;
+    public float2 texcoord;
+    public Sampler2D backbuffer;
 }
diff --git a/kitty/shaders/slang.py b/kitty/shaders/slang.py
index 1469e9f09..937a23ede 100644
--- a/kitty/shaders/slang.py
+++ b/kitty/shaders/slang.py
@@ -968,7 +968,7 @@ def build_custom_shader_pipeline_ir(slot: str = 'after-window-background', shade
             entry_points.append(entry_point)
         mod_src = get_custom_shader_src('pipeline').decode()
         mod_src = mod_src.replace('// IMPORTS', '\n'.join(f'__include "{w}";' for w in wrappers), 1)
-        mod_src = mod_src.replace('// PIPELINE', '\n'.join(f'color = {w}(color, vo.d);' for w in entry_points), 1)
+        mod_src = mod_src.replace('// PIPELINE', '\n'.join(f'color = {w}(color, d);' for w in entry_points), 1)
         # subprocess.run(['bat', '-P', '-l', 'cpp'], input=mod_src.encode())
         slot_key = key(slot, mod_src, shaders_content_key)