From 09a6bcfffc24f5abdc8709403bab7ae1e01563f1 Mon Sep 17 00:00:00 2001
From: Héctor Ramón Jiménez <hector@hecrj.dev>
Date: Thu, 2 May 2024 13:15:17 +0200
Subject: Add `Image` rotation support

Co-authored-by: DKolter <68352124+DKolter@users.noreply.github.com>
---
 wgpu/src/shader/image.wgsl | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

(limited to 'wgpu/src/shader')

diff --git a/wgpu/src/shader/image.wgsl b/wgpu/src/shader/image.wgsl
index 7b2e5238..de962098 100644
--- a/wgpu/src/shader/image.wgsl
+++ b/wgpu/src/shader/image.wgsl
@@ -9,10 +9,13 @@ struct Globals {
 struct VertexInput {
     @builtin(vertex_index) vertex_index: u32,
     @location(0) pos: vec2<f32>,
-    @location(1) scale: vec2<f32>,
-    @location(2) atlas_pos: vec2<f32>,
-    @location(3) atlas_scale: vec2<f32>,
-    @location(4) layer: i32,
+    @location(1) center: vec2<f32>,
+    @location(2) image_size: vec2<f32>,
+    @location(3) rotation: f32,
+    @location(4) scale: vec2<f32>,
+    @location(5) atlas_pos: vec2<f32>,
+    @location(6) atlas_scale: vec2<f32>,
+    @location(7) layer: i32,
 }
 
 struct VertexOutput {
@@ -25,24 +28,42 @@ struct VertexOutput {
 fn vs_main(input: VertexInput) -> VertexOutput {
     var out: VertexOutput;
 
-    let v_pos = vertex_position(input.vertex_index);
+    // Generate a vertex position in the range [0, 1] from the vertex index.
+    var v_pos = vertex_position(input.vertex_index);
 
+    // Map the vertex position to the atlas texture.
     out.uv = vec2<f32>(v_pos * input.atlas_scale + input.atlas_pos);
     out.layer = f32(input.layer);
 
-    var transform: mat4x4<f32> = mat4x4<f32>(
+    // Calculate the vertex position and move the center to the origin
+    v_pos = input.pos + v_pos * input.image_size - input.center;
+
+    // Apply the rotation around the center of the image
+    let cos_rot = cos(input.rotation);
+    let sin_rot = sin(input.rotation);
+    let rotate = mat4x4<f32>(
+        vec4<f32>(cos_rot, sin_rot, 0.0, 0.0),
+        vec4<f32>(-sin_rot, cos_rot, 0.0, 0.0),
+        vec4<f32>(0.0, 0.0, 1.0, 0.0),
+        vec4<f32>(0.0, 0.0, 0.0, 1.0)
+    );
+
+    // Scale the image and then translate to the final position by moving the center to the position
+    let scale_translate = mat4x4<f32>(
         vec4<f32>(input.scale.x, 0.0, 0.0, 0.0),
         vec4<f32>(0.0, input.scale.y, 0.0, 0.0),
         vec4<f32>(0.0, 0.0, 1.0, 0.0),
-        vec4<f32>(input.pos, 0.0, 1.0)
+        vec4<f32>(input.center, 0.0, 1.0)
     );
 
-    out.position = globals.transform * transform * vec4<f32>(v_pos, 0.0, 1.0);
+    // Calculate the final position of the vertex
+    out.position = globals.transform * scale_translate * rotate * vec4<f32>(v_pos, 0.0, 1.0);
 
     return out;
 }
 
 @fragment
 fn fs_main(input: VertexOutput) -> @location(0) vec4<f32> {
+    // Sample the texture at the given UV coordinate and layer.
     return textureSample(u_texture, u_sampler, input.uv, i32(input.layer));
 }
-- 
cgit