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// SPDX-License-Identifier: Unlicense OR MIT
package opengl
import (
"errors"
"fmt"
"image"
"runtime"
"strings"
"gioui.org/internal/byteslice"
"gioui.org/internal/gl"
)
// SRGBFBO implements an intermediate sRGB FBO
// for gamma-correct rendering on platforms without
// sRGB enabled native framebuffers.
type SRGBFBO struct {
c *gl.Functions
state *glState
viewport image.Point
fbo gl.Framebuffer
tex gl.Texture
blitted bool
quad gl.Buffer
prog gl.Program
format textureTriple
}
func NewSRGBFBO(f *gl.Functions, state *glState) (*SRGBFBO, error) {
glVer := f.GetString(gl.VERSION)
ver, _, err := gl.ParseGLVersion(glVer)
if err != nil {
return nil, err
}
exts := strings.Split(f.GetString(gl.EXTENSIONS), " ")
srgbTriple, err := srgbaTripleFor(ver, exts)
if err != nil {
// Fall back to the linear RGB colorspace, at the cost of color precision loss.
srgbTriple = textureTriple{gl.RGBA, gl.Enum(gl.RGBA), gl.Enum(gl.UNSIGNED_BYTE)}
}
s := &SRGBFBO{
c: f,
state: state,
format: srgbTriple,
fbo: f.CreateFramebuffer(),
tex: f.CreateTexture(),
}
state.bindTexture(f, 0, s.tex)
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 *SRGBFBO) Blit() {
if !s.blitted {
prog, err := gl.CreateProgram(s.c, blitVSrc, blitFSrc, []string{"pos", "uv"})
if err != nil {
panic(err)
}
s.prog = prog
s.state.useProgram(s.c, prog)
s.c.Uniform1i(s.c.GetUniformLocation(prog, "tex"), 0)
s.quad = s.c.CreateBuffer()
s.state.bindBuffer(s.c, gl.ARRAY_BUFFER, s.quad)
coords := byteslice.Slice([]float32{
-1, +1, 0, 1,
+1, +1, 1, 1,
-1, -1, 0, 0,
+1, -1, 1, 0,
})
s.c.BufferData(gl.ARRAY_BUFFER, len(coords), gl.STATIC_DRAW, coords)
s.blitted = true
}
s.state.useProgram(s.c, s.prog)
s.state.bindTexture(s.c, 0, s.tex)
s.state.vertexAttribPointer(s.c, s.quad, 0 /* pos */, 2, gl.FLOAT, false, 4*4, 0)
s.state.vertexAttribPointer(s.c, s.quad, 1 /* uv */, 2, gl.FLOAT, false, 4*4, 4*2)
s.state.setVertexAttribArray(s.c, 0, true)
s.state.setVertexAttribArray(s.c, 1, true)
s.c.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
s.state.bindFramebuffer(s.c, gl.FRAMEBUFFER, s.fbo)
s.c.InvalidateFramebuffer(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0)
}
func (s *SRGBFBO) Framebuffer() gl.Framebuffer {
return s.fbo
}
func (s *SRGBFBO) Refresh(viewport image.Point) error {
if viewport.X == 0 || viewport.Y == 0 {
return errors.New("srgb: zero-sized framebuffer")
}
if s.viewport == viewport {
return nil
}
s.viewport = viewport
s.state.bindTexture(s.c, 0, s.tex)
s.c.TexImage2D(gl.TEXTURE_2D, 0, s.format.internalFormat, viewport.X, viewport.Y, s.format.format, s.format.typ)
s.state.bindFramebuffer(s.c, gl.FRAMEBUFFER, s.fbo)
s.c.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, s.tex, 0)
if st := s.c.CheckFramebufferStatus(gl.FRAMEBUFFER); st != gl.FRAMEBUFFER_COMPLETE {
return fmt.Errorf("sRGB framebuffer incomplete (%dx%d), status: %#x error: %x", viewport.X, viewport.Y, 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.state.setClearColor(s.c, .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, viewport.X, viewport.Y, gl.RGBA, gl.UNSIGNED_BYTE)
if st := s.c.CheckFramebufferStatus(gl.FRAMEBUFFER); st != gl.FRAMEBUFFER_COMPLETE {
return fmt.Errorf("fallback RGBA framebuffer incomplete (%dx%d), status: %#x error: %x", viewport.X, viewport.Y, st, s.c.GetError())
}
}
}
return nil
}
func (s *SRGBFBO) Release() {
s.state.deleteFramebuffer(s.c, s.fbo)
s.state.deleteTexture(s.c, s.tex)
if s.blitted {
s.state.deleteBuffer(s.c, s.quad)
s.state.deleteProgram(s.c, 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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