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// SPDX-License-Identifier: Unlicense OR MIT
package srgb
import (
"fmt"
"runtime"
"strings"
"gioui.org/app/internal/glimpl"
"gioui.org/gpu/gl"
"gioui.org/internal/unsafe"
)
// FBO implements an intermediate sRGB FBO
// for gamma-correct rendering on platforms without
// sRGB enabled native framebuffers.
type FBO struct {
c *glimpl.Functions
width, height int
frameBuffer gl.Framebuffer
depthBuffer gl.Renderbuffer
colorTex gl.Texture
blitted bool
quad gl.Buffer
prog gl.Program
gl3 bool
}
func New(f *glimpl.Functions) (*FBO, error) {
var gl3 bool
glVer := f.GetString(gl.VERSION)
ver, _, err := gl.ParseGLVersion(glVer)
if err != nil {
return nil, err
}
if ver[0] >= 3 {
gl3 = true
} else {
exts := f.GetString(gl.EXTENSIONS)
if !strings.Contains(exts, "EXT_sRGB") {
return nil, fmt.Errorf("no support for OpenGL ES 3 nor EXT_sRGB")
}
}
s := &FBO{
c: f,
gl3: gl3,
frameBuffer: f.CreateFramebuffer(),
colorTex: f.CreateTexture(),
depthBuffer: f.CreateRenderbuffer(),
}
f.BindTexture(gl.TEXTURE_2D, s.colorTex)
f.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
f.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
f.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
f.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
return s, nil
}
func (s *FBO) Blit() {
if !s.blitted {
prog, err := gl.CreateProgram(s.c, blitVSrc, blitFSrc, []string{"pos", "uv"})
if err != nil {
panic(err)
}
s.prog = prog
s.c.UseProgram(prog)
s.c.Uniform1i(gl.GetUniformLocation(s.c, prog, "tex"), 0)
s.quad = s.c.CreateBuffer()
s.c.BindBuffer(gl.ARRAY_BUFFER, s.quad)
s.c.BufferData(gl.ARRAY_BUFFER,
unsafe.BytesView([]float32{
-1, +1, 0, 1,
+1, +1, 1, 1,
-1, -1, 0, 0,
+1, -1, 1, 0,
}),
gl.STATIC_DRAW)
s.blitted = true
}
s.c.BindFramebuffer(gl.FRAMEBUFFER, gl.Framebuffer{})
s.c.UseProgram(s.prog)
s.c.BindTexture(gl.TEXTURE_2D, s.colorTex)
s.c.BindBuffer(gl.ARRAY_BUFFER, s.quad)
s.c.VertexAttribPointer(0 /* pos */, 2, gl.FLOAT, false, 4*4, 0)
s.c.VertexAttribPointer(1 /* uv */, 2, gl.FLOAT, false, 4*4, 4*2)
s.c.EnableVertexAttribArray(0)
s.c.EnableVertexAttribArray(1)
s.c.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
s.c.BindTexture(gl.TEXTURE_2D, gl.Texture{})
s.c.DisableVertexAttribArray(0)
s.c.DisableVertexAttribArray(1)
s.c.BindFramebuffer(gl.FRAMEBUFFER, s.frameBuffer)
s.c.InvalidateFramebuffer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0)
s.c.InvalidateFramebuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT)
// The Android emulator requires framebuffer 0 bound at eglSwapBuffer time.
// Bind the sRGB framebuffer again in afterPresent.
s.c.BindFramebuffer(gl.FRAMEBUFFER, gl.Framebuffer{})
}
func (s *FBO) AfterPresent() {
s.c.BindFramebuffer(gl.FRAMEBUFFER, s.frameBuffer)
}
func (s *FBO) Refresh(w, h int) error {
s.width, s.height = w, h
if w == 0 || h == 0 {
return nil
}
s.c.BindTexture(gl.TEXTURE_2D, s.colorTex)
if s.gl3 {
s.c.TexImage2D(gl.TEXTURE_2D, 0, gl.SRGB8_ALPHA8, w, h, gl.RGBA, gl.UNSIGNED_BYTE, nil)
} else /* EXT_sRGB */ {
s.c.TexImage2D(gl.TEXTURE_2D, 0, gl.SRGB_ALPHA_EXT, w, h, gl.SRGB_ALPHA_EXT, gl.UNSIGNED_BYTE, nil)
}
currentRB := gl.Renderbuffer(s.c.GetBinding(gl.RENDERBUFFER_BINDING))
s.c.BindRenderbuffer(gl.RENDERBUFFER, s.depthBuffer)
s.c.RenderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, w, h)
s.c.BindRenderbuffer(gl.RENDERBUFFER, currentRB)
s.c.BindFramebuffer(gl.FRAMEBUFFER, s.frameBuffer)
s.c.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, s.colorTex, 0)
s.c.FramebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, s.depthBuffer)
if st := s.c.CheckFramebufferStatus(gl.FRAMEBUFFER); st != gl.FRAMEBUFFER_COMPLETE {
return fmt.Errorf("sRGB framebuffer incomplete (%dx%d), status: %#x error: %x", s.width, s.height, st, s.c.GetError())
}
if runtime.GOOS == "js" {
// With macOS Safari, rendering to and then reading from a SRGB8_ALPHA8
// texture result in twice gamma corrected colors. Using a plain RGBA
// texture seems to work.
s.c.ClearColor(.5, .5, .5, 1.0)
s.c.Clear(gl.COLOR_BUFFER_BIT)
var pixel [4]byte
s.c.ReadPixels(0, 0, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel[:])
if pixel[0] == 128 { // Correct sRGB color value is ~188
s.c.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, w, h, gl.RGBA, gl.UNSIGNED_BYTE, nil)
if st := s.c.CheckFramebufferStatus(gl.FRAMEBUFFER); st != gl.FRAMEBUFFER_COMPLETE {
return fmt.Errorf("fallback RGBA framebuffer incomplete (%dx%d), status: %#x error: %x", s.width, s.height, st, s.c.GetError())
}
}
}
return nil
}
func (s *FBO) Release() {
s.c.DeleteFramebuffer(s.frameBuffer)
s.c.DeleteTexture(s.colorTex)
s.c.DeleteRenderbuffer(s.depthBuffer)
if s.blitted {
s.c.DeleteBuffer(s.quad)
s.c.DeleteProgram(s.prog)
}
s.c = nil
}
const (
blitVSrc = `
#version 100
precision highp float;
attribute vec2 pos;
attribute vec2 uv;
varying vec2 vUV;
void main() {
gl_Position = vec4(pos, 0, 1);
vUV = uv;
}
`
blitFSrc = `
#version 100
precision mediump float;
uniform sampler2D tex;
varying vec2 vUV;
vec3 gamma(vec3 rgb) {
vec3 exp = vec3(1.055)*pow(rgb, vec3(0.41666)) - vec3(0.055);
vec3 lin = rgb * vec3(12.92);
bvec3 cut = lessThan(rgb, vec3(0.0031308));
return vec3(cut.r ? lin.r : exp.r, cut.g ? lin.g : exp.g, cut.b ? lin.b : exp.b);
}
void main() {
vec4 col = texture2D(tex, vUV);
vec3 rgb = col.rgb;
rgb = gamma(rgb);
gl_FragColor = vec4(rgb, col.a);
}
`
)
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