gpu,app,internal/glimpl: update GL backend for the compute renderer

Modern graphics APIs have immutable objects, with mutable data. For example,
a texture's dimensions are immutable, while the texture contents is not.
Change the GPU API abstraction to match.

Clearing a Texture is convenient to do with a plain []byte. Generalize
Texture.Upload to take a plain byte slice and introduce a helper function for
uploading *image.RGBA data.

Add TextureFormatRGBA8 a format for the linear RGB colorspace.

Add OpenGL ES 3.1 functions for compute programs.

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

internal/glimpl/gl.go

@@ -8,19 +8,24 @@ type (
 )
 
 const (
+	ALL_BARRIER_BITS                      = 0xffffffff
 	ARRAY_BUFFER                          = 0x8892
 	BLEND                                 = 0xbe2
 	CLAMP_TO_EDGE                         = 0x812f
 	COLOR_ATTACHMENT0                     = 0x8ce0
 	COLOR_BUFFER_BIT                      = 0x4000
 	COMPILE_STATUS                        = 0x8b81
+	COMPUTE_SHADER                        = 0x91B9
 	DEPTH_BUFFER_BIT                      = 0x100
 	DEPTH_ATTACHMENT                      = 0x8d00
 	DEPTH_COMPONENT16                     = 0x81a5
 	DEPTH_COMPONENT24                     = 0x81A6
 	DEPTH_COMPONENT32F                    = 0x8CAC
 	DEPTH_TEST                            = 0xb71
+	DRAW_FRAMEBUFFER                      = 0x8CA9
 	DST_COLOR                             = 0x306
+	DYNAMIC_DRAW                          = 0x88E8
+	DYNAMIC_READ                          = 0x88E9
 	ELEMENT_ARRAY_BUFFER                  = 0x8893
 	EXTENSIONS                            = 0x1f03
 	FALSE                                 = 0
@@ -39,6 +44,7 @@ const (
 	LINEAR                                = 0x2601
 	LINK_STATUS                           = 0x8b82
 	LUMINANCE                             = 0x1909
+	MAP_READ_BIT                          = 0x0001
 	MAX_TEXTURE_SIZE                      = 0xd33
 	NEAREST                               = 0x2600
 	NO_ERROR                              = 0x0
@@ -50,6 +56,8 @@ const (
 	R16F                                  = 0x822d
 	R8                                    = 0x8229
 	READ_FRAMEBUFFER                      = 0x8ca8
+	READ_ONLY                             = 0x88B8
+	READ_WRITE                            = 0x88BA
 	RED                                   = 0x1903
 	RENDERER                              = 0x1F01
 	RENDERBUFFER                          = 0x8d41
@@ -59,12 +67,14 @@ const (
 	RGB                                   = 0x1907
 	RGBA                                  = 0x1908
 	RGBA8                                 = 0x8058
+	SHADER_STORAGE_BUFFER                 = 0x90D2
 	SHORT                                 = 0x1402
 	SRGB                                  = 0x8c40
 	SRGB_ALPHA_EXT                        = 0x8c42
 	SRGB8                                 = 0x8c41
 	SRGB8_ALPHA8                          = 0x8c43
 	STATIC_DRAW                           = 0x88e4
+	STENCIL_BUFFER_BIT                    = 0x00000400
 	TEXTURE_2D                            = 0xde1
 	TEXTURE_MAG_FILTER                    = 0x2800
 	TEXTURE_MIN_FILTER                    = 0x2801
@@ -81,6 +91,7 @@ const (
 	UNSIGNED_SHORT                        = 0x1403
 	VERSION                               = 0x1f02
 	VERTEX_SHADER                         = 0x8b31
+	WRITE_ONLY                            = 0x88B9
 	ZERO                                  = 0x0
 
 	// EXT_disjoint_timer_query
@@ -96,11 +107,14 @@ var _ interface {
 	BindBuffer(target Enum, b Buffer)
 	BindBufferBase(target Enum, index int, buffer Buffer)
 	BindFramebuffer(target Enum, fb Framebuffer)
+	BindImageTexture(unit int, t Texture, level int, layered bool, layer int, access, format Enum)
 	BindRenderbuffer(target Enum, fb Renderbuffer)
 	BindTexture(target Enum, t Texture)
 	BlendEquation(mode Enum)
 	BlendFunc(sfactor, dfactor Enum)
-	BufferData(target Enum, src []byte, usage Enum)
+	BlitFramebuffer(sx0, sy0, sx1, sy1, dx0, dy0, dx1, dy1 int, mask Enum, filter Enum)
+	BufferData(target Enum, size int, usage Enum)
+	BufferSubData(target Enum, offset int, src []byte)
 	CheckFramebufferStatus(target Enum) Enum
 	Clear(mask Enum)
 	ClearColor(red, green, blue, alpha float32)
@@ -124,6 +138,7 @@ var _ interface {
 	DepthMask(mask bool)
 	DisableVertexAttribArray(a Attrib)
 	Disable(cap Enum)
+	DispatchCompute(x, y, z int)
 	DrawArrays(mode Enum, first, count int)
 	DrawElements(mode Enum, count int, ty Enum, offset int)
 	Enable(cap Enum)
@@ -144,11 +159,15 @@ var _ interface {
 	GetUniformLocation(p Program, name string) Uniform
 	InvalidateFramebuffer(target, attachment Enum)
 	LinkProgram(p Program)
+	MapBufferRange(target Enum, offset, length int, access Enum) []byte
+	MemoryBarrier(barriers Enum)
 	ReadPixels(x, y, width, height int, format, ty Enum, data []byte)
 	RenderbufferStorage(target, internalformat Enum, width, height int)
 	ShaderSource(s Shader, src string)
-	TexImage2D(target Enum, level int, internalFormat int, width, height int, format, ty Enum, data []byte)
+	TexImage2D(target Enum, level int, internalFormat Enum, width, height int, format, ty Enum)
 	TexParameteri(target, pname Enum, param int)
+	TexStorage2D(target Enum, levels int, internalFormat Enum, width, height int)
+	TexSubImage2D(target Enum, level, xoff, yoff int, width, height int, format, ty Enum, data []byte)
 	UniformBlockBinding(p Program, uniformBlockIndex uint, uniformBlockBinding uint)
 	Uniform1f(dst Uniform, v float32)
 	Uniform1i(dst Uniform, v int)
@@ -156,6 +175,7 @@ var _ interface {
 	Uniform3f(dst Uniform, v0, v1, v2 float32)
 	Uniform4f(dst Uniform, v0, v1, v2, v3 float32)
 	UseProgram(p Program)
+	UnmapBuffer(target Enum) bool
 	VertexAttribPointer(dst Attrib, size int, ty Enum, normalized bool, stride, offset int)
 	Viewport(x, y, width, height int)
 } = (*Functions)(nil)