internal/shaderir: revert the refactoring to generalize the memory layout logic

Unfortunately, the memory layout was not so universal. For example,
the memory layout for mat2 is different between Metal and DirectX.

internal/graphicsdriver/directx/graphics11_windows.go

@@ -513,7 +513,7 @@ func (g *graphics11) NewShader(program *shaderir.Program) (graphicsdriver.Shader
 		graphics:         g,
 		id:               g.genNextShaderID(),
 		uniformTypes:     program.Uniforms,
-		uniformOffsets:   hlsl.CalcUniformMemoryOffsetsInDWords(program),
+		uniformOffsets:   hlsl.UniformVariableOffsetsInDWords(program),
 		vertexShaderBlob: vsh,
 		pixelShaderBlob:  psh,
 	}

internal/graphicsdriver/directx/graphics12_windows.go

@@ -1073,7 +1073,7 @@ func (g *graphics12) NewShader(program *shaderir.Program) (graphicsdriver.Shader
 		graphics:       g,
 		id:             g.genNextShaderID(),
 		uniformTypes:   program.Uniforms,
-		uniformOffsets: hlsl.CalcUniformMemoryOffsetsInDWords(program),
+		uniformOffsets: hlsl.UniformVariableOffsetsInDWords(program),
 		vertexShader:   vsh,
 		pixelShader:    psh,
 	}

internal/shaderir/hlsl/hlsl.go

@@ -81,7 +81,7 @@ float4x4 float4x4FromScalar(float x) {
 }`
 
 func Compile(p *shaderir.Program) (vertexShader, pixelShader, prelude string) {
-	offsets := CalcUniformMemoryOffsetsInDWords(p)
+	offsets := UniformVariableOffsetsInDWords(p)
 
 	c := &compileContext{
 		unit: p.Unit,
@@ -119,8 +119,8 @@ func Compile(p *shaderir.Program) (vertexShader, pixelShader, prelude string) {
 		lines = append(lines, "cbuffer Uniforms : register(b0) {")
 		for i, t := range p.Uniforms {
 			// packingoffset is not mandatory, but this is useful to ensure the correct offset is used.
-			offset := fmt.Sprintf("c%d", offsets[i]/boundaryInDWords)
-			switch offsets[i] % boundaryInDWords {
+			offset := fmt.Sprintf("c%d", offsets[i]/UniformVariableBoundaryInDWords)
+			switch offsets[i] % UniformVariableBoundaryInDWords {
 			case 1:
 				offset += ".y"
 			case 2:

internal/shaderir/hlsl/uniform.go

@@ -20,22 +20,23 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
 )
 
-const boundaryInDWords = 4
+const UniformVariableBoundaryInDWords = 4
 
-func CalcUniformMemoryOffsetsInDWords(program *shaderir.Program) []int {
+// UniformVariableOffsetsInDWords returns the offsets of the uniform variables in DWROD units in the HLSL layout.
+func UniformVariableOffsetsInDWords(program *shaderir.Program) []int {
 	// https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-packing-rules
 	// https://github.com/microsoft/DirectXShaderCompiler/wiki/Buffer-Packing
 
-	var offsetsInDWords []int
-	var headInDWords int
-
 	align := func(x int) int {
 		if x == 0 {
 			return 0
 		}
-		return ((x-1)/boundaryInDWords + 1) * boundaryInDWords
+		return ((x-1)/UniformVariableBoundaryInDWords + 1) * UniformVariableBoundaryInDWords
 	}
 
+	var offsetsInDWords []int
+	var headInDWords int
+
 	// TODO: Reorder the variables with packoffset.
 	// See https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-variable-packoffset
 	for _, u := range program.Uniforms {
@@ -47,19 +48,19 @@ func CalcUniformMemoryOffsetsInDWords(program *shaderir.Program) []int {
 			offsetsInDWords = append(offsetsInDWords, headInDWords)
 			headInDWords += 1
 		case shaderir.Vec2, shaderir.IVec2:
-			if headInDWords%boundaryInDWords >= 3 {
+			if headInDWords%UniformVariableBoundaryInDWords >= 3 {
 				headInDWords = align(headInDWords)
 			}
 			offsetsInDWords = append(offsetsInDWords, headInDWords)
 			headInDWords += 2
 		case shaderir.Vec3, shaderir.IVec3:
-			if headInDWords%boundaryInDWords >= 2 {
+			if headInDWords%UniformVariableBoundaryInDWords >= 2 {
 				headInDWords = align(headInDWords)
 			}
 			offsetsInDWords = append(offsetsInDWords, headInDWords)
 			headInDWords += 3
 		case shaderir.Vec4, shaderir.IVec4:
-			if headInDWords%boundaryInDWords >= 1 {
+			if headInDWords%UniformVariableBoundaryInDWords >= 1 {
 				headInDWords = align(headInDWords)
 			}
 			offsetsInDWords = append(offsetsInDWords, headInDWords)