gpu: expose the rendering implementation

The rendering implementation is needed for using Gio UI with external
window libraries such as GLFW. Expose it in the new package gpu.

Updates #26

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

gpu/timer.go

@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package gpu
+
+import (
+	"time"
+
+	"gioui.org/gpu/gl"
+)
+
+type timers struct {
+	ctx    *context
+	timers []*timer
+}
+
+type timer struct {
+	Elapsed time.Duration
+	ctx     *context
+	obj     gl.Query
+	state   timerState
+}
+
+type timerState uint8
+
+const (
+	timerIdle timerState = iota
+	timerRunning
+	timerWaiting
+)
+
+func newTimers(ctx *context) *timers {
+	return &timers{
+		ctx: ctx,
+	}
+}
+
+func (t *timers) newTimer() *timer {
+	if t == nil {
+		return nil
+	}
+	tt := &timer{
+		ctx: t.ctx,
+		obj: t.ctx.CreateQuery(),
+	}
+	t.timers = append(t.timers, tt)
+	return tt
+}
+
+func (t *timer) begin() {
+	if t == nil || t.state != timerIdle {
+		return
+	}
+	t.ctx.BeginQuery(gl.TIME_ELAPSED_EXT, t.obj)
+	t.state = timerRunning
+}
+
+func (t *timer) end() {
+	if t == nil || t.state != timerRunning {
+		return
+	}
+	t.ctx.EndQuery(gl.TIME_ELAPSED_EXT)
+	t.state = timerWaiting
+}
+
+func (t *timers) ready() bool {
+	if t == nil {
+		return false
+	}
+	for _, tt := range t.timers {
+		if tt.state != timerWaiting {
+			return false
+		}
+		if t.ctx.GetQueryObjectuiv(tt.obj, gl.QUERY_RESULT_AVAILABLE) == 0 {
+			return false
+		}
+	}
+	for _, tt := range t.timers {
+		tt.state = timerIdle
+		nanos := t.ctx.GetQueryObjectuiv(tt.obj, gl.QUERY_RESULT)
+		tt.Elapsed = time.Duration(nanos)
+	}
+	return t.ctx.GetInteger(gl.GPU_DISJOINT_EXT) == 0
+}
+
+func (t *timers) release() {
+	if t == nil {
+		return
+	}
+	for _, tt := range t.timers {
+		t.ctx.DeleteQuery(tt.obj)
+	}
+	t.timers = nil
+}