gpu/internal/opengl: support sRGB emulation for desktop OpenGL

Desktop OpenGL implements a GL_FRAMEBUFFER_SRGB setting; query that instead
of the frambuffer color encoding.

With this change it is no longer necessary to enable FRAMEBUFFER_SRGB
in the macOS setup; remove it.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/wm/gl_macos.m

@@ -84,5 +84,4 @@ void gio_prepareContext(void) {
 	GLuint defVBA;
 	glGenVertexArrays(1, &defVBA);
 	glBindVertexArray(defVBA);
-	glEnable(GL_FRAMEBUFFER_SRGB);
 }

gpu/internal/opengl/opengl.go

@@ -33,8 +33,9 @@ type Backend struct {
 	alphaTriple textureTriple
 	srgbaTriple textureTriple
 
-	sRGBFBO *srgb.FBO
+	sRGBFBO     *srgb.FBO
-	defFBO  gl.Framebuffer
+	enabledSRGB bool
+	defFBO      gl.Framebuffer
 }
 
 // State tracking.
@@ -177,27 +178,33 @@ func (b *Backend) BeginFrame(clear bool, viewport image.Point) driver.Framebuffe
 	// Assume GL state is reset between frames.
 	b.state = glstate{}
 	b.defFBO = gl.Framebuffer(b.funcs.GetBinding(gl.FRAMEBUFFER_BINDING))
-	// Determine color encoding of the output framebuffer.
-	var fbEncoding int
-	if !b.defFBO.Valid() {
-		fbEncoding = b.funcs.GetFramebufferAttachmentParameteri(gl.FRAMEBUFFER, gl.BACK, gl.FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING)
-	} else {
-		fbEncoding = b.funcs.GetFramebufferAttachmentParameteri(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING)
-	}
 	renderFBO := b.defFBO
-	if fbEncoding == gl.LINEAR {
+	if b.gles {
-		if b.sRGBFBO == nil {
+		// If the output framebuffer is not in the sRGB colorspace already, emulate it.
-			// Framebuffer is not in sRGB format. Emulate it.
+		var fbEncoding int
-			sfbo, err := srgb.New(b.funcs)
+		if !b.defFBO.Valid() {
-			if err != nil {
+			fbEncoding = b.funcs.GetFramebufferAttachmentParameteri(gl.FRAMEBUFFER, gl.BACK, gl.FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING)
+		} else {
+			fbEncoding = b.funcs.GetFramebufferAttachmentParameteri(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING)
+		}
+		if fbEncoding == gl.LINEAR {
+			if b.sRGBFBO == nil {
+				sfbo, err := srgb.New(b.funcs)
+				if err != nil {
+					panic(err)
+				}
+				b.sRGBFBO = sfbo
+			}
+			if err := b.sRGBFBO.Refresh(viewport); err != nil {
 				panic(err)
 			}
-			b.sRGBFBO = sfbo
+			renderFBO = b.sRGBFBO.Framebuffer()
 		}
-		if err := b.sRGBFBO.Refresh(viewport); err != nil {
+	} else {
-			panic(err)
+		b.enabledSRGB = !b.funcs.IsEnabled(gl.FRAMEBUFFER_SRGB)
+		if b.enabledSRGB {
+			b.funcs.Enable(gl.FRAMEBUFFER_SRGB)
 		}
-		renderFBO = b.sRGBFBO.Framebuffer()
 	}
 	b.funcs.BindFramebuffer(gl.FRAMEBUFFER, renderFBO)
 	if b.sRGBFBO != nil && !clear {
@@ -220,6 +227,9 @@ func (b *Backend) EndFrame() {
 	}
 	b.SetBlend(false)
 	b.funcs.BindFramebuffer(gl.FRAMEBUFFER, b.defFBO)
+	if b.enabledSRGB {
+		b.funcs.Disable(gl.FRAMEBUFFER_SRGB)
+	}
 }
 
 func (b *Backend) Caps() driver.Caps {

internal/gl/gl.go

@@ -36,6 +36,7 @@ const (
 	FRAMEBUFFER_ATTACHMENT_COLOR_ENCODING = 0x8210
 	FRAMEBUFFER_BINDING                   = 0x8ca6
 	FRAMEBUFFER_COMPLETE                  = 0x8cd5
+	FRAMEBUFFER_SRGB                      = 0x8db9
 	HALF_FLOAT                            = 0x140b
 	HALF_FLOAT_OES                        = 0x8d61
 	INFO_LOG_LENGTH                       = 0x8B84

internal/gl/gl_js.go

@@ -276,6 +276,9 @@ func (f *Functions) InvalidateFramebuffer(target, attachment Enum) {
 		f.Ctx.Call("invalidateFramebuffer", int(target), f.int32Buf)
 	}
 }
+func (f *Functions) IsEnabled(cap Enum) bool {
+	return f.Ctx.Call("isEnabled", int(cap)).Truthy()
+}
 func (f *Functions) LinkProgram(p Program) {
 	f.Ctx.Call("linkProgram", js.Value(p))
 }

internal/gl/gl_unix.go

@@ -83,6 +83,7 @@ typedef struct {
 	void (*glGetShaderInfoLog)(GLuint shader, GLsizei bufSize, GLsizei *length, GLchar *infoLog);
 	const GLubyte *(*glGetString)(GLenum name);
 	GLint (*glGetUniformLocation)(GLuint program, const GLchar *name);
+	GLboolean (*glIsEnabled)(GLenum cap);
 	void (*glLinkProgram)(GLuint program);
 	void (*glPixelStorei)(GLenum pname, GLint param);
 	void (*glReadPixels)(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, void *pixels);
@@ -319,6 +320,10 @@ static GLint glGetUniformLocation(glFunctions *f, GLuint program, const GLchar *
 	return f->glGetUniformLocation(program, name);
 }
 
+static GLboolean glIsEnabled(glFunctions *f, GLenum cap) {
+	return f->glIsEnabled(cap);
+}
+
 static void glLinkProgram(glFunctions *f, GLuint program) {
 	f->glLinkProgram(program);
 }
@@ -588,6 +593,7 @@ func (f *Functions) load(forceES bool) error {
 	f.f.glGetShaderInfoLog = must("glGetShaderInfoLog")
 	f.f.glGetString = must("glGetString")
 	f.f.glGetUniformLocation = must("glGetUniformLocation")
+	f.f.glIsEnabled = must("glIsEnabled")
 	f.f.glLinkProgram = must("glLinkProgram")
 	f.f.glPixelStorei = must("glPixelStorei")
 	f.f.glReadPixels = must("glReadPixels")
@@ -980,6 +986,10 @@ func (f *Functions) InvalidateFramebuffer(target, attachment Enum) {
 	C.glInvalidateFramebuffer(&f.f, C.GLenum(target), C.GLenum(attachment))
 }
 
+func (f *Functions) IsEnabled(cap Enum) bool {
+	return C.glIsEnabled(&f.f, C.GLenum(cap)) == TRUE
+}
+
 func (f *Functions) LinkProgram(p Program) {
 	C.glLinkProgram(&f.f, C.GLuint(p.V))
 }

internal/gl/gl_windows.go

@@ -70,6 +70,7 @@ var (
 	_glGetString                          = LibGLESv2.NewProc("glGetString")
 	_glGetUniformLocation                 = LibGLESv2.NewProc("glGetUniformLocation")
 	_glInvalidateFramebuffer              = LibGLESv2.NewProc("glInvalidateFramebuffer")
+	_glIsEnabled                          = LibGLESv2.NewProc("glIsEnabled")
 	_glLinkProgram                        = LibGLESv2.NewProc("glLinkProgram")
 	_glPixelStorei                        = LibGLESv2.NewProc("glPixelStorei")
 	_glReadPixels                         = LibGLESv2.NewProc("glReadPixels")
@@ -347,6 +348,10 @@ func (c *Functions) InvalidateFramebuffer(target, attachment Enum) {
 	}
 	syscall.Syscall(addr, 3, uintptr(target), 1, uintptr(unsafe.Pointer(&attachment)))
 }
+func (f *Functions) IsEnabled(cap Enum) bool {
+	u, _, _ := syscall.Syscall(_glIsEnabled.Addr(), 1, uintptr(cap), 0, 0)
+	return u == TRUE
+}
 func (c *Functions) LinkProgram(p Program) {
 	syscall.Syscall(_glLinkProgram.Addr(), 1, uintptr(p.V), 0, 0)
 }