internal/shaderir/glfw: Insert a dummy function to touch uniform array variables

Closes #1754

internal/shaderir/glsl/glsl.go

@@ -147,9 +147,45 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 			}
 		}
 
+		// Add a dummy function to just touch uniform array variable's elements (#1754).
+		// Without this, the first elements of a uniform array might not be initialized correctly on some environments.
+		var touchedUniforms []string
+		for i, t := range p.Uniforms {
+			if t.Main != shaderir.Array {
+				continue
+			}
+			if t.Length <= 1 {
+				continue
+			}
+			str := fmt.Sprintf("U%d[%d]", i, t.Length-1)
+			switch t.Sub[0].Main {
+			case shaderir.Vec2, shaderir.Vec3, shaderir.Vec4:
+				str += ".x"
+			case shaderir.Mat2, shaderir.Mat3, shaderir.Mat4:
+				str += "[0][0]"
+			}
+			str = "float(" + str + ")"
+			touchedUniforms = append(touchedUniforms, str)
+		}
+
+		var touchUniformsFunc []string
+		if len(touchedUniforms) > 0 {
+			touchUniformsFunc = append(touchUniformsFunc, "float touchUniforms() {")
+			touchUniformsFunc = append(touchUniformsFunc, fmt.Sprintf("\treturn %s;", strings.Join(touchedUniforms, " + ")))
+			touchUniformsFunc = append(touchUniformsFunc, "}")
+
+		}
+
 		if p.VertexFunc.Block != nil && len(p.VertexFunc.Block.Stmts) > 0 {
+			if len(touchUniformsFunc) > 0 {
+				vslines = append(vslines, "")
+				vslines = append(vslines, touchUniformsFunc...)
+			}
 			vslines = append(vslines, "")
 			vslines = append(vslines, "void main(void) {")
+			if len(touchUniformsFunc) > 0 {
+				vslines = append(vslines, "\ttouchUniforms();")
+			}
 			vslines = append(vslines, c.glslBlock(p, p.VertexFunc.Block, p.VertexFunc.Block, 0)...)
 			vslines = append(vslines, "}")
 		}

shader_test.go

@@ -1111,3 +1111,72 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 		}
 	}
 }
+
+// Issue #1754
+func TestShaderUniformFirstElement(t *testing.T) {
+	shaders := []struct {
+		Name     string
+		Shader   string
+		Uniforms map[string]interface{}
+	}{
+		{
+			Name: "float array",
+			Shader: `package main
+
+var C [2]float
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return vec4(C[0], 1, 1, 1)
+}`,
+			Uniforms: map[string]interface{}{
+				"C": []float32{1, 1},
+			},
+		},
+		{
+			Name: "float one-element array",
+			Shader: `package main
+
+var C [1]float
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return vec4(C[0], 1, 1, 1)
+}`,
+			Uniforms: map[string]interface{}{
+				"C": []float32{1},
+			},
+		},
+		{
+			Name: "matrix array",
+			Shader: `package main
+
+var C [2]mat2
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return vec4(C[0][0][0], 1, 1, 1)
+}`,
+			Uniforms: map[string]interface{}{
+				"C": []float32{1, 0, 0, 0, 0, 0, 0, 0},
+			},
+		},
+	}
+
+	for _, shader := range shaders {
+		shader := shader
+		t.Run(shader.Name, func(t *testing.T) {
+			const w, h = 1, 1
+
+			dst := NewImage(w, h)
+			s, err := NewShader([]byte(shader.Shader))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			op := &DrawRectShaderOptions{}
+			op.Uniforms = shader.Uniforms
+			dst.DrawRectShader(w, h, s, op)
+			if got, want := dst.At(0, 0), (color.RGBA{0xff, 0xff, 0xff, 0xff}); got != want {
+				t.Errorf("got: %v, want: %v", got, want)
+			}
+		})
+	}
+}