gpu: implement automatic mipmaps for images

All GPU APIs except OpenGL ES 2 can generate mipmaps for textures.
This trades 33% more GPU memory use for improved rendering quality
and speed for downscaled images.

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

internal/gl/gl.go

@@ -56,6 +56,7 @@ const (
 	GREATER                               = 0x204
 	GEQUAL                                = 0x206
 	LINEAR                                = 0x2601
+	LINEAR_MIPMAP_LINEAR                  = 0x2703
 	LINK_STATUS                           = 0x8b82
 	LUMINANCE                             = 0x1909
 	MAP_READ_BIT                          = 0x0001

internal/gl/gl_js.go

@@ -72,6 +72,7 @@ type Functions struct {
 	_flush                             js.Value
 	_framebufferRenderbuffer           js.Value
 	_framebufferTexture2D              js.Value
+	_generateMipmap                    js.Value
 	_getRenderbufferParameteri         js.Value
 	_getFramebufferAttachmentParameter js.Value
 	_getParameter                      js.Value
@@ -167,6 +168,7 @@ func NewFunctions(ctx Context, forceES bool) (*Functions, error) {
 		_flush:                             _bind(webgl, `flush`),
 		_framebufferRenderbuffer:           _bind(webgl, `framebufferRenderbuffer`),
 		_framebufferTexture2D:              _bind(webgl, `framebufferTexture2D`),
+		_generateMipmap:                    _bind(webgl, `generateMipmap`),
 		_getRenderbufferParameteri:         _bind(webgl, `getRenderbufferParameteri`),
 		_getFramebufferAttachmentParameter: _bind(webgl, `getFramebufferAttachmentParameter`),
 		_getParameter:                      _bind(webgl, `getParameter`),
@@ -419,6 +421,9 @@ func (f *Functions) FramebufferRenderbuffer(target, attachment, renderbuffertarg
 func (f *Functions) FramebufferTexture2D(target, attachment, texTarget Enum, t Texture, level int) {
 	f._framebufferTexture2D.Invoke(int(target), int(attachment), int(texTarget), js.Value(t), level)
 }
+func (f *Functions) GenerateMipmap(target Enum) {
+	f._generateMipmap.Invoke(int(target))
+}
 func (f *Functions) GetError() Enum {
 	// Avoid slow getError calls. See gio#179.
 	return 0

internal/gl/gl_unix.go

@@ -72,6 +72,7 @@ typedef void (*_glFlush)(void);
 typedef void (*_glFramebufferRenderbuffer)(GLenum target, GLenum attachment, GLenum renderbuffertarget, GLuint renderbuffer);
 typedef void (*_glFramebufferTexture2D)(GLenum target, GLenum attachment, GLenum textarget, GLuint texture, GLint level);
 typedef void (*_glGenBuffers)(GLsizei n, GLuint *buffers);
+typedef void (*_glGenerateMipmap)(GLenum target);
 typedef void (*_glGenFramebuffers)(GLsizei n, GLuint *framebuffers);
 typedef void (*_glGenRenderbuffers)(GLsizei n, GLuint *renderbuffers);
 typedef void (*_glGenTextures)(GLsizei n, GLuint *textures);
@@ -286,6 +287,10 @@ static void glGenBuffers(_glGenBuffers f, GLsizei n, GLuint *buffers) {
 	f(n, buffers);
 }
 
+static void glGenerateMipmap(_glGenerateMipmap f, GLenum target) {
+	f(target);
+}
+
 static void glGenFramebuffers(_glGenFramebuffers f, GLsizei n, GLuint *framebuffers) {
 	f(n, framebuffers);
 }
@@ -561,6 +566,7 @@ type Functions struct {
 	glFramebufferRenderbuffer             C._glFramebufferRenderbuffer
 	glFramebufferTexture2D                C._glFramebufferTexture2D
 	glGenBuffers                          C._glGenBuffers
+	glGenerateMipmap                      C._glGenerateMipmap
 	glGenFramebuffers                     C._glGenFramebuffers
 	glGenRenderbuffers                    C._glGenRenderbuffers
 	glGenTextures                         C._glGenTextures
@@ -723,6 +729,7 @@ func (f *Functions) load(forceES bool) error {
 	f.glFramebufferRenderbuffer = must("glFramebufferRenderbuffer")
 	f.glFramebufferTexture2D = must("glFramebufferTexture2D")
 	f.glGenBuffers = must("glGenBuffers")
+	f.glGenerateMipmap = must("glGenerateMipmap")
 	f.glGenFramebuffers = must("glGenFramebuffers")
 	f.glGenRenderbuffers = must("glGenRenderbuffers")
 	f.glGenTextures = must("glGenTextures")
@@ -1048,6 +1055,10 @@ func (f *Functions) FramebufferTexture2D(target, attachment, texTarget Enum, t T
 	C.glFramebufferTexture2D(f.glFramebufferTexture2D, C.GLenum(target), C.GLenum(attachment), C.GLenum(texTarget), C.GLuint(t.V), C.GLint(level))
 }
 
+func (f *Functions) GenerateMipmap(target Enum) {
+	C.glGenerateMipmap(f.glGenerateMipmap, C.GLenum(target))
+}
+
 func (c *Functions) GetBinding(pname Enum) Object {
 	return Object{uint(c.GetInteger(pname))}
 }

internal/gl/gl_windows.go

@@ -35,6 +35,7 @@ var (
 	_glDeleteVertexArrays                  = LibGLESv2.NewProc("glDeleteVertexArrays")
 	_glCompileShader                       = LibGLESv2.NewProc("glCompileShader")
 	_glCopyTexSubImage2D                   = LibGLESv2.NewProc("glCopyTexSubImage2D")
+	_glGenerateMipmap                      = LibGLESv2.NewProc("glGenerateMipmap")
 	_glGenBuffers                          = LibGLESv2.NewProc("glGenBuffers")
 	_glGenFramebuffers                     = LibGLESv2.NewProc("glGenFramebuffers")
 	_glGenVertexArrays                     = LibGLESv2.NewProc("glGenVertexArrays")
@@ -192,6 +193,9 @@ func (c *Functions) CompileShader(s Shader) {
 func (f *Functions) CopyTexSubImage2D(target Enum, level, xoffset, yoffset, x, y, width, height int) {
 	syscall.Syscall9(_glCopyTexSubImage2D.Addr(), 8, uintptr(target), uintptr(level), uintptr(xoffset), uintptr(yoffset), uintptr(x), uintptr(y), uintptr(width), uintptr(height), 0)
 }
+func (f *Functions) GenerateMipmap(target Enum) {
+	syscall.Syscall(_glGenerateMipmap.Addr(), 1, uintptr(target), 0, 0)
+}
 func (c *Functions) CreateBuffer() Buffer {
 	var buf uintptr
 	syscall.Syscall(_glGenBuffers.Addr(), 2, 1, uintptr(unsafe.Pointer(&buf)), 0)