gpu: Merge GPU.Collect and GPU.Frame

There's no meaningful reason to have them separate. The intention was to
enable rendering concurrent with other processing, but that's gaining
framerate at the expense of input latency and complicating ImageOp
semantics.

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

app/loop.go

@@ -97,10 +97,9 @@ func (l *renderLoop) renderLoop(ctx wm.Context) error {
 				} else {
 					g.Clear(color.NRGBA{A: 0xff, R: 0xff, G: 0xff, B: 0xff})
 				}
-				g.Collect(frame.viewport, frame.ops)
+				res.err = g.Frame(frame.ops, ctx.RenderTarget(), frame.viewport)
 				// Signal that we're done with the frame ops.
 				l.ack <- struct{}{}
-				res.err = g.Frame(ctx.RenderTarget())
 				if res.err == nil {
 					res.err = ctx.Present()
 				}

gpu/compute.go

@@ -559,7 +559,12 @@ func newShaders(ctx driver.Device, vsrc, fsrc shader.Sources) (vert driver.Verte
 	return
 }
 
-func (g *compute) Collect(viewport image.Point, ops *op.Ops) {
+func (g *compute) Frame(frameOps *op.Ops, target RenderTarget, viewport image.Point) error {
+	g.collect(viewport, frameOps)
+	return g.frame(target)
+}
+
+func (g *compute) collect(viewport image.Point, ops *op.Ops) {
 	g.viewport = viewport
 	g.collector.reset()
 	for i := range g.output.layerAtlases {
@@ -575,7 +580,7 @@ func (g *compute) Clear(col color.NRGBA) {
 	g.collector.clearColor = f32color.LinearFromSRGB(col)
 }
 
-func (g *compute) Frame(target RenderTarget) error {
+func (g *compute) frame(target RenderTarget) error {
 	viewport := g.viewport
 	defFBO := g.ctx.BeginFrame(target, g.collector.clear, viewport)
 	defer g.ctx.EndFrame()

gpu/gpu.go

@@ -43,12 +43,10 @@ type GPU interface {
 	Release()
 	// Clear sets the clear color for the next Frame.
 	Clear(color color.NRGBA)
-	// Collect the graphics operations from frame, given the viewport.
+	// Frame draws the graphics operations from op into a viewport of target.
-	Collect(viewport image.Point, frame *op.Ops)
+	Frame(frame *op.Ops, target RenderTarget, viewport image.Point) error
-	// Frame draws the collected operations to target.
-	Frame(target RenderTarget) error
 	// Profile returns the last available profiling information. Profiling
-	// information is requested when Collect sees an io/profile.Op, and the result
+	// information is requested when Frame sees an io/profile.Op, and the result
 	// is available through Profile at some later time.
 	Profile() string
 }
@@ -399,7 +397,12 @@ func (g *gpu) Release() {
 	g.ctx.Release()
 }
 
-func (g *gpu) Collect(viewport image.Point, frameOps *op.Ops) {
+func (g *gpu) Frame(frameOps *op.Ops, target RenderTarget, viewport image.Point) error {
+	g.collect(viewport, frameOps)
+	return g.frame(target)
+}
+
+func (g *gpu) collect(viewport image.Point, frameOps *op.Ops) {
 	g.renderer.blitter.viewport = viewport
 	g.renderer.pather.viewport = viewport
 	g.drawOps.reset(g.cache, viewport)
@@ -413,7 +416,7 @@ func (g *gpu) Collect(viewport image.Point, frameOps *op.Ops) {
 	}
 }
 
-func (g *gpu) Frame(target RenderTarget) error {
+func (g *gpu) frame(target RenderTarget) error {
 	viewport := g.renderer.blitter.viewport
 	defFBO := g.ctx.BeginFrame(target, g.drawOps.clear, viewport)
 	defer g.ctx.EndFrame()

gpu/headless/headless.go

@@ -109,8 +109,7 @@ func (w *Window) Release() {
 func (w *Window) Frame(frame *op.Ops) error {
 	return contextDo(w.ctx, func() error {
 		w.gpu.Clear(color.NRGBA{})
-		w.gpu.Collect(w.size, frame)
+		return w.gpu.Frame(frame, driver.RenderTarget(w.fbo), w.size)
-		return w.gpu.Frame(driver.RenderTarget(w.fbo))
 	})
 }
 

io/system/system.go

@@ -26,27 +26,8 @@ type FrameEvent struct {
 	Size image.Point
 	// Insets is the insets to apply.
 	Insets Insets
-	// Frame is the callback to supply the list of
+	// Frame completes the FrameEvent by drawing the graphical operations
-	// operations to complete the FrameEvent.
+	// from ops into the window.
-	//
-	// Note that the operation list and the operations themselves
-	// may not be mutated until another FrameEvent is received from
-	// the same event source.
-	// That means that calls to frame.Reset and changes to referenced
-	// data such as ImageOp backing images should happen between
-	// receiving a FrameEvent and calling Frame.
-	//
-	// Example:
-	//
-	//  var w *app.Window
-	//  var frame *op.Ops
-	//  for e := range w.Events() {
-	//      if e, ok := e.(system.FrameEvent); ok {
-	//          // Call frame.Reset and manipulate images for ImageOps
-	//          // here.
-	//          e.Frame(frame)
-	//      }
-	//  }
 	Frame func(frame *op.Ops)
 	// Queue supplies the events for event handlers.
 	Queue event.Queue

op/paint/paint.go

@@ -16,9 +16,6 @@ import (
 )
 
 // ImageOp sets the brush to an image.
-//
-// Note: the ImageOp may keep a reference to the backing image.
-// See NewImageOp for details.
 type ImageOp struct {
 	uniform bool
 	color   color.NRGBA
@@ -47,9 +44,7 @@ type LinearGradientOp struct {
 type PaintOp struct {
 }
 
-// NewImageOp creates an ImageOp backed by src. See
+// NewImageOp creates an ImageOp backed by src.
-// gioui.org/io/system.FrameEvent for a description of when data
-// referenced by operations is safe to re-use.
 //
 // NewImageOp assumes the backing image is immutable, and may cache a
 // copy of its contents in a GPU-friendly way. Create new ImageOps to