From 800be4f77223fb78fec0d3a8e611d3000c02454e Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Tue, 26 Nov 2024 12:19:27 +0900
Subject: [PATCH] ebiten: add test for matrix indices

---
 .../graphicsdriver/directx/shader_windows.go  |  3 ++
 .../graphicsdriver/metal/graphics_darwin.go   |  2 +-
 shader_test.go                                | 40 +++++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/internal/graphicsdriver/directx/shader_windows.go b/internal/graphicsdriver/directx/shader_windows.go
index cec20d1a7..4af2cff52 100644
--- a/internal/graphicsdriver/directx/shader_windows.go
+++ b/internal/graphicsdriver/directx/shader_windows.go
@@ -199,6 +199,9 @@ func constantBufferSize(uniformTypes []shaderir.Type, uniformOffsets []int) int
 }
 
 func adjustUniforms(uniformTypes []shaderir.Type, uniformOffsets []int, uniforms []uint32) []uint32 {
+	// Note that HLSL's matrices are row-major, while GLSL and MSL are column-major.
+	// Transpose matrices so that users can access matrix indices in the same way as GLSL and MSL.
+
 	var fs []uint32
 	var idx int
 	for i, typ := range uniformTypes {
diff --git a/internal/graphicsdriver/metal/graphics_darwin.go b/internal/graphicsdriver/metal/graphics_darwin.go
index 69c99c366..0b0e57c5c 100644
--- a/internal/graphicsdriver/metal/graphics_darwin.go
+++ b/internal/graphicsdriver/metal/graphics_darwin.go
@@ -909,11 +909,11 @@ func adjustUniformVariablesLayout(uniformTypes []shaderir.Type, uniforms []uint3
 			values = append(values, 0)
 		case shaderir.Mat4:
 			values = fillZerosToFitAlignment(values, 4)
-			u := uniforms[idx : idx+16]
 			if i == graphics.ProjectionMatrixUniformVariableIndex {
 				// In Metal, the NDC's Y direction (upward) and the framebuffer's Y direction (downward) don't
 				// match. Then, the Y direction must be inverted.
 				// Invert the sign bits as float32 values.
+				u := uniforms[idx : idx+16]
 				values = append(values,
 					u[0], u[1]^uint32(1<<31), u[2], u[3],
 					u[4], u[5]^uint32(1<<31), u[6], u[7],
diff --git a/shader_test.go b/shader_test.go
index 954838ee5..b1b8a5dbc 100644
--- a/shader_test.go
+++ b/shader_test.go
@@ -1097,6 +1097,46 @@ func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
 	}
 }
 
+func TestShaderUniformMatrixIndexer(t *testing.T) {
+	const w, h = 16, 16
+
+	dst := ebiten.NewImage(w, h)
+	s, err := ebiten.NewShader([]byte(`//kage:unit pixels
+
+package main
+
+var Mat4 mat4
+
+func Fragment(dstPos vec4, srcPos vec2, color vec4) vec4 {
+	return Mat4[1][2] * vec4(1)
+}
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	op := &ebiten.DrawRectShaderOptions{}
+	op.Uniforms = map[string]any{
+		"Mat4": []float32{
+			1.0 / 256.0, 2.0 / 256.0, 3.0 / 256.0, 4.0 / 256.0,
+			5.0 / 256.0, 6.0 / 256.0, 7.0 / 256.0, 8.0 / 256.0,
+			9.0 / 256.0, 10.0 / 256.0, 11.0 / 256.0, 12.0 / 256.0,
+			13.0 / 256.0, 14.0 / 256.0, 15.0 / 256.0, 16.0 / 256.0,
+		},
+	}
+	dst.DrawRectShader(w, h, s, op)
+
+	for j := 0; j < h; j++ {
+		for i := 0; i < w; i++ {
+			got := dst.At(i, j).(color.RGBA)
+			want := color.RGBA{R: 7, G: 7, B: 7, A: 7}
+			if !sameColors(got, want, 2) {
+				t.Errorf("dst.At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+		}
+	}
+}
+
 func TestShaderOptionsNegativeBounds(t *testing.T) {
 	const w, h = 16, 16