5 files changed, 82 insertions, 0 deletions
diff --git a/src/effects/scratch.wgsl b/src/effects/scratch.wgsl
new file mode 100644
index 0000000..818202e
--- /dev/null
+++ b/src/effects/scratch.wgsl
@@ -0,0 +1,14 @@
+// Scratch effect - overlays film scratch lines on top of the input buffer
+#include "sequence_uniforms"
+#include "render/fullscreen_uv_vs"
+#include "render/scratch_lines"
+
+@group(0) @binding(0) var input_sampler: sampler;
+@group(0) @binding(1) var input_texture: texture_2d<f32>;
+@group(0) @binding(2) var<uniform> uniforms: UniformsSequenceParams;
+
+@fragment fn fs_main(in: VertexOutput) -> @location(0) vec4f {
+    let color = textureSample(input_texture, input_sampler, in.uv);
+    let s = scratch_lines(in.uv, uniforms.resolution, uniforms.time);
+    return vec4f(color.rgb + vec3f(s), color.a);
+}
diff --git a/src/effects/scratch_effect.cc b/src/effects/scratch_effect.cc
new file mode 100644
index 0000000..f49e601
--- /dev/null
+++ b/src/effects/scratch_effect.cc
@@ -0,0 +1,44 @@
+// Scratch effect - film scratch overlay post-process
+
+#include "effects/scratch_effect.h"
+#include "effects/shaders.h"
+#include "gpu/post_process_helper.h"
+#include "util/fatal_error.h"
+
+Scratch::Scratch(const GpuContext& ctx, const std::vector<std::string>& inputs,
+                 const std::vector<std::string>& outputs, float start_time,
+                 float end_time)
+    : Effect(ctx, inputs, outputs, start_time, end_time) {
+  HEADLESS_RETURN_IF_NULL(ctx_.device);
+
+  create_linear_sampler();
+
+  pipeline_.set(create_post_process_pipeline(ctx_.device,
+                                             WGPUTextureFormat_RGBA8Unorm,
+                                             scratch_shader_wgsl));
+}
+
+void Scratch::render(WGPUCommandEncoder encoder,
+                     const UniformsSequenceParams& params,
+                     NodeRegistry& nodes) {
+  WGPUTextureView input_view = nodes.get_view(input_nodes_[0]);
+  WGPUTextureView output_view = nodes.get_view(output_nodes_[0]);
+
+  pp_update_bind_group(ctx_.device, pipeline_.get(), bind_group_.get_address(),
+                       input_view, uniforms_buffer_.get(), {nullptr, 0});
+
+  WGPURenderPassColorAttachment color_attachment = {};
+  gpu_init_color_attachment(color_attachment, output_view);
+
+  WGPURenderPassDescriptor pass_desc = {};
+  pass_desc.colorAttachmentCount = 1;
+  pass_desc.colorAttachments = &color_attachment;
+
+  WGPURenderPassEncoder pass =
+      wgpuCommandEncoderBeginRenderPass(encoder, &pass_desc);
+  wgpuRenderPassEncoderSetPipeline(pass, pipeline_.get());
+  wgpuRenderPassEncoderSetBindGroup(pass, 0, bind_group_.get(), 0, nullptr);
+  wgpuRenderPassEncoderDraw(pass, 3, 1, 0, 0);
+  wgpuRenderPassEncoderEnd(pass);
+  wgpuRenderPassEncoderRelease(pass);
+}
diff --git a/src/effects/scratch_effect.h b/src/effects/scratch_effect.h
new file mode 100644
index 0000000..fb36a96
--- /dev/null
+++ b/src/effects/scratch_effect.h
@@ -0,0 +1,20 @@
+// Scratch effect - film scratch overlay post-process
+// Reads input buffer, additively blends scratch_lines() on top.
+
+#pragma once
+#include "gpu/effect.h"
+#include "gpu/wgpu_resource.h"
+
+class Scratch : public Effect {
+ public:
+  Scratch(const GpuContext& ctx, const std::vector<std::string>& inputs,
+          const std::vector<std::string>& outputs, float start_time,
+          float end_time);
+
+  void render(WGPUCommandEncoder encoder, const UniformsSequenceParams& params,
+              NodeRegistry& nodes) override;
+
+ private:
+  RenderPipeline pipeline_;
+  BindGroup bind_group_;
+};
diff --git a/src/effects/shaders.cc b/src/effects/shaders.cc
index c6a81d0..e4b9b25 100644
--- a/src/effects/shaders.cc
+++ b/src/effects/shaders.cc
@@ -51,6 +51,8 @@ void InitShaderComposer() {
   register_if_exists("ray_box", AssetId::ASSET_SHADER_RAY_BOX);
   register_if_exists("ray_triangle", AssetId::ASSET_SHADER_RAY_TRIANGLE);
 
+  register_if_exists("render/scratch_lines",
+                     AssetId::ASSET_SHADER_RENDER_SCRATCH_LINES);
   register_if_exists("render/fullscreen_vs",
                      AssetId::ASSET_SHADER_RENDER_FULLSCREEN_VS);
   register_if_exists("render/fullscreen_uv_vs",
@@ -97,6 +99,7 @@ const char* rotating_cube_wgsl =
 const char* flash_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_FLASH);
 const char* scene1_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_SCENE1);
 const char* scene2_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_SCENE2);
+const char* scratch_shader_wgsl = SafeGetAsset(AssetId::ASSET_SHADER_SCRATCH);
 
 // Compute shaders
 const char* gen_noise_compute_wgsl =
diff --git a/src/effects/shaders.h b/src/effects/shaders.h
index 5fc442a..76b5d96 100644
--- a/src/effects/shaders.h
+++ b/src/effects/shaders.h
@@ -16,6 +16,7 @@ extern const char* rotating_cube_wgsl;
 extern const char* flash_shader_wgsl;
 extern const char* scene1_shader_wgsl;
 extern const char* scene2_shader_wgsl;
+extern const char* scratch_shader_wgsl;
 
 // Compute shaders
 extern const char* gen_noise_compute_wgsl;