gl: download ANGLE if necessary

For golang/go#9306

Change-Id: Ibb469d843d2bddeaa3690c59bc9ad532ea3473f7
Reviewed-on: https://go-review.googlesource.com/17810
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

gl/dll_windows.go

@@ -0,0 +1,163 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gl
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+var debug = log.New(ioutil.Discard, "gl: ", log.LstdFlags)
+
+func downloadDLLs() (path string, err error) {
+	url := "https://dl.google.com/go/mobile/angle-dd5c5b-" + runtime.GOARCH + ".tgz"
+	debug.Printf("downloading %s", url)
+	resp, err := http.Get(url)
+	if err != nil {
+		return "", fmt.Errorf("gl: %v", err)
+	}
+	defer func() {
+		err2 := resp.Body.Close()
+		if err == nil && err2 != nil {
+			err = fmt.Errorf("gl: error reading body from %v: %v", url, err2)
+		}
+	}()
+	if resp.StatusCode != http.StatusOK {
+		err := fmt.Errorf("gl: error fetching %v, status: %v", url, resp.Status)
+		return "", err
+	}
+
+	r, err := gzip.NewReader(resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("gl: error reading gzip from %v: %v", url, err)
+	}
+	tr := tar.NewReader(r)
+	var bytesGLESv2, bytesEGL []byte
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return "", fmt.Errorf("gl: error reading tar from %v: %v", url, err)
+		}
+		switch header.Name {
+		case "angle-" + runtime.GOARCH + "/libglesv2.dll":
+			bytesGLESv2, err = ioutil.ReadAll(tr)
+		case "angle-" + runtime.GOARCH + "/libegl.dll":
+			bytesEGL, err = ioutil.ReadAll(tr)
+		default: // skip
+		}
+		if err != nil {
+			return "", fmt.Errorf("gl: error reading %v from %v: %v", header.Name, url, err)
+		}
+	}
+	if len(bytesGLESv2) == 0 || len(bytesEGL) == 0 {
+		return "", fmt.Errorf("gl: did not find both DLLs in %v", url)
+	}
+
+	writeDLLs := func(path string) error {
+		if err := ioutil.WriteFile(filepath.Join(path, "libglesv2.dll"), bytesGLESv2, 0755); err != nil {
+			return fmt.Errorf("gl: cannot install ANGLE: %v", err)
+		}
+		if err := ioutil.WriteFile(filepath.Join(path, "libegl.dll"), bytesEGL, 0755); err != nil {
+			return fmt.Errorf("gl: cannot install ANGLE: %v", err)
+		}
+		return nil
+	}
+
+	// First, we attempt to install these DLLs in LOCALAPPDATA/Shiny.
+	//
+	// Traditionally we would use the system32 directory, but it is
+	// no longer writable by normal programs.
+	os.MkdirAll(appdataPath(), 0775)
+	if err := writeDLLs(appdataPath()); err == nil {
+		return appdataPath(), nil
+	}
+	debug.Printf("DLLs could not be written to %s", appdataPath())
+
+	// Second, install in GOPATH/pkg if it exists.
+	gopath := os.Getenv("GOPATH")
+	gopathpkg := filepath.Join(gopath, "pkg")
+	if _, err := os.Stat(gopathpkg); err == nil && gopath != "" {
+		if err := writeDLLs(gopathpkg); err == nil {
+			return gopathpkg, nil
+		}
+	}
+	debug.Printf("DLLs could not be written to GOPATH")
+
+	// Third, pick a temporary directory.
+	tmp := os.TempDir()
+	if err := writeDLLs(tmp); err != nil {
+		return "", fmt.Errorf("gl: unable to install ANGLE DLLs: %v", err)
+	}
+	return tmp, nil
+}
+
+func appdataPath() string {
+	return filepath.Join(os.Getenv("LOCALAPPDATA"), "GoGL", runtime.GOARCH)
+}
+
+func findDLLs() (err error) {
+	load := func(path string) (bool, error) {
+		if path != "" {
+			LibGLESv2.Name = filepath.Join(path, filepath.Base(LibGLESv2.Name))
+			LibEGL.Name = filepath.Join(path, filepath.Base(LibEGL.Name))
+		}
+		if err := LibGLESv2.Load(); err == nil {
+			if err := LibEGL.Load(); err != nil {
+				return false, fmt.Errorf("gl: loaded libglesv2 but not libegl: %v", err)
+			}
+			if path == "" {
+				debug.Printf("DLLs found")
+			} else {
+				debug.Printf("DLLs found in: %q", path)
+			}
+			return true, nil
+		}
+		return false, nil
+	}
+
+	// Look in the system directory.
+	if ok, err := load(""); ok || err != nil {
+		return err
+	}
+
+	// Look in the AppData directory.
+	if ok, err := load(appdataPath()); ok || err != nil {
+		return err
+	}
+
+	// TODO: Look for a Chrome installation.
+
+	// Look in GOPATH/pkg.
+	if ok, err := load(filepath.Join(os.Getenv("GOPATH"), "pkg")); ok || err != nil {
+		return err
+	}
+
+	// Look in temporary directory.
+	if ok, err := load(os.TempDir()); ok || err != nil {
+		return err
+	}
+
+	// Download the DLL binary.
+	path, err := downloadDLLs()
+	if err != nil {
+		return err
+	}
+	debug.Printf("DLLs written to %s", path)
+	if ok, err := load(path); !ok || err != nil {
+		return fmt.Errorf("gl: unable to load ANGLE after installation: %v", err)
+	}
+	return nil
+}

gl/work_windows.go

@@ -24,6 +24,9 @@ type context struct {
 func (ctx *context) WorkAvailable() <-chan struct{} { return ctx.workAvailable }
 
 func NewContext() (Context, Worker) {
+	if err := findDLLs(); err != nil {
+		panic(err)
+	}
 	glctx := &context{
 		workAvailable: make(chan struct{}, 1),
 		work:          make(chan call, 3),
@@ -393,10 +396,17 @@ func (ctx *context) doWork(c call) (ret uintptr) {
 	return ret
 }
 
-// TODO: export LibGLESv2/LibEGL lazy DLLs, and come up with a loading scheme.
+// Exported libraries for a Windows GUI driver.
+//
+// LibEGL is not used directly by the gl package, but is needed by any
+// driver hoping to use OpenGL ES.
+var (
+	LibGLESv2 = syscall.NewLazyDLL("libglesv2.dll")
+	LibEGL    = syscall.NewLazyDLL("libegl.dll")
+)
 
 var (
-	libGLESv2                             = syscall.NewLazyDLL("libGLESv2.dll")
+	libGLESv2                             = LibGLESv2
 	glActiveTexture                       = libGLESv2.NewProc("glActiveTexture")
 	glAttachShader                        = libGLESv2.NewProc("glAttachShader")
 	glBindAttribLocation                  = libGLESv2.NewProc("glBindAttribLocation")