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headless.go
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headless.go
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// SPDX-License-Identifier: Unlicense OR MIT
// Package headless implements headless windows for rendering
// an operation list to an image.
package headless
import (
"image"
"runtime"
"gioui.org/gpu"
"gioui.org/gpu/backend"
"gioui.org/op"
)
// Window is a headless window.
type Window struct {
size image.Point
ctx context
backend backend.Device
gpu *gpu.GPU
fboTex backend.Texture
fbo backend.Framebuffer
}
type context interface {
Backend() (backend.Device, error)
MakeCurrent() error
ReleaseCurrent()
Release()
}
// NewWindow creates a new headless window.
func NewWindow(width, height int) (*Window, error) {
ctx, err := newContext()
if err != nil {
return nil, err
}
w := &Window{
size: image.Point{X: width, Y: height},
ctx: ctx,
}
err = contextDo(ctx, func() error {
dev, err := ctx.Backend()
if err != nil {
return err
}
dev.Viewport(0, 0, width, height)
fboTex, err := dev.NewTexture(
backend.TextureFormatSRGB,
width, height,
backend.FilterNearest, backend.FilterNearest,
backend.BufferBindingFramebuffer,
)
if err != nil {
return nil
}
const depthBits = 16
fbo, err := dev.NewFramebuffer(fboTex, depthBits)
if err != nil {
fboTex.Release()
return err
}
dev.BindFramebuffer(fbo)
gp, err := gpu.New(dev)
if err != nil {
fbo.Release()
fboTex.Release()
return err
}
w.fboTex = fboTex
w.fbo = fbo
w.gpu = gp
w.backend = dev
return err
})
if err != nil {
ctx.Release()
return nil, err
}
return w, nil
}
// Release resources associated with the window.
func (w *Window) Release() {
contextDo(w.ctx, func() error {
if w.fbo != nil {
w.fbo.Release()
w.fbo = nil
}
if w.fboTex != nil {
w.fboTex.Release()
w.fboTex = nil
}
if w.gpu != nil {
w.gpu.Release()
w.gpu = nil
}
return nil
})
if w.ctx != nil {
w.ctx.Release()
w.ctx = nil
}
}
// Frame replace the window content and state with the
// operation list.
func (w *Window) Frame(frame *op.Ops) {
contextDo(w.ctx, func() error {
w.gpu.Collect(w.size, frame)
w.gpu.BeginFrame()
w.gpu.EndFrame()
return nil
})
}
// Screenshot returns an image with the content of the window.
func (w *Window) Screenshot() (*image.RGBA, error) {
img := image.NewRGBA(image.Rectangle{Max: w.size})
err := contextDo(w.ctx, func() error {
return w.fbo.ReadPixels(
image.Rectangle{
Max: image.Point{X: w.size.X, Y: w.size.Y},
}, img.Pix)
})
if err != nil {
return nil, err
}
return img, nil
}
func contextDo(ctx context, f func() error) error {
errCh := make(chan error)
go func() {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
if err := ctx.MakeCurrent(); err != nil {
errCh <- err
return
}
defer ctx.ReleaseCurrent()
errCh <- f()
}()
return <-errCh
}