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>

app/internal/window/gl_ios.go

@@ -16,8 +16,8 @@ import (
 	"errors"
 	"fmt"
 
-	"gioui.org/app/internal/gl"
-	"gioui.org/app/internal/gl/impl"
+	"gioui.org/gpu/gl"
+	"gioui.org/app/internal/glimpl"
 )
 
 type context struct {
@@ -45,7 +45,7 @@ func newContext(w *window) (*context, error) {
 		ctx:   ctx,
 		owner: w,
 		layer: C.CFTypeRef(w.contextLayer()),
-		c:     new(impl.Functions),
+		c:     new(glimpl.Functions),
 	}
 	return c, nil
 }

app/internal/window/gl_js.go

@@ -6,8 +6,8 @@ import (
 	"errors"
 	"syscall/js"
 
-	"gioui.org/app/internal/gl"
-	"gioui.org/app/internal/gl/impl"
+	"gioui.org/gpu/gl"
+	"gioui.org/app/internal/glimpl"
 )
 
 type context struct {
@@ -33,7 +33,7 @@ func newContext(w *window) (*context, error) {
 	if ctx.IsNull() {
 		return nil, errors.New("app: webgl is not supported")
 	}
-	f := &impl.Functions{Ctx: ctx}
+	f := &glimpl.Functions{Ctx: ctx}
 	if err := f.Init(version); err != nil {
 		return nil, err
 	}

app/internal/window/gl_macos.go

@@ -5,8 +5,8 @@
 package window
 
 import (
-	"gioui.org/app/internal/gl"
-	"gioui.org/app/internal/gl/impl"
+	"gioui.org/gpu/gl"
+	"gioui.org/app/internal/glimpl"
 )
 
 /*
@@ -35,7 +35,7 @@ func newContext(w *window) (*context, error) {
 	ctx := C.gio_contextForView(view)
 	c := &context{
 		ctx:  ctx,
-		c:    new(impl.Functions),
+		c:    new(glimpl.Functions),
 		view: view,
 	}
 	return c, nil

app/internal/window/window.go

@@ -9,7 +9,7 @@ import (
 	"math"
 	"time"
 
-	"gioui.org/app/internal/gl"
+	"gioui.org/gpu/gl"
 	"gioui.org/io/event"
 	"gioui.org/io/system"
 	"gioui.org/unit"