ebiten/internal/glfw/load_windows.go

// Copyright 2018 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package glfw

import (
	"bytes"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"unsafe"

	"golang.org/x/sys/windows"
)

type dll struct {
	d     *windows.LazyDLL
	procs map[string]*windows.LazyProc
}

func (d *dll) call(name string, args ...uintptr) uintptr {
	if d.procs == nil {
		d.procs = map[string]*windows.LazyProc{}
	}
	if _, ok := d.procs[name]; !ok {
		d.procs[name] = d.d.NewProc(name)
	}
	r, _, err := d.procs[name].Call(args...)
	if err != nil && err.(windows.Errno) != 0 {
		// It looks like there is no way to handle these errors?
		// panic(fmt.Sprintf("glfw: calling proc error: errno: %d (%s)", err, err.Error()))
	}
	return r
}

func writeDLLFile(name string) error {
	f, err := gzip.NewReader(bytes.NewReader(glfwDLLCompressed))
	if err != nil {
		return err
	}
	defer f.Close()

	out, err := os.Create(name)
	if err != nil {
		return err
	}
	defer out.Close()

	if _, err := io.Copy(out, f); err != nil {
		return err
	}
	return nil
}

func loadDLL() (*dll, error) {
	cachedir, err := os.UserCacheDir()
	if err != nil {
		return nil, err
	}

	dir := filepath.Join(cachedir, "ebiten")
	if err := os.MkdirAll(dir, 0755); err != nil {
		return nil, err
	}

	fn := filepath.Join(dir, glfwDLLHash+".dll")
	if _, err := os.Stat(fn); err != nil {
		if !os.IsNotExist(err) {
			return nil, err
		}

		// Create a DLL as a temporary file and then rename it later.
		// Without the temporary file, writing a DLL might fail in the process of writing and Ebiten cannot
		// notice that the DLL file is incomplete.
		if err := writeDLLFile(fn + ".tmp"); err != nil {
			return nil, err
		}

		if err := os.Rename(fn+".tmp", fn); err != nil {
			return nil, err
		}
	}

	return &dll{
		d: windows.NewLazyDLL(fn),
	}, nil
}

func (d *dll) unload() error {
	if err := windows.FreeLibrary(windows.Handle(d.d.Handle())); err != nil {
		return err
	}
	return nil
}

func bytePtrToString(ptr *byte) string {
	var bs []byte
	for i := uintptr(0); ; i++ {
		b := *(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(ptr)) + i))
		if b == 0 {
			break
		}
		bs = append(bs, b)
	}
	return string(bs)
}

type glfwError struct {
	code ErrorCode
	desc string
}

func (e *glfwError) Error() string {
	return fmt.Sprintf("glfw: %s: %s", e.code.String(), e.desc)
}

var lastErr = make(chan *glfwError, 1)

func fetchError() error {
	select {
	case err := <-lastErr:
		return err
	default:
		return nil
	}
}

func panicError() {
	if err := acceptError(); err != nil {
		panic(err)
	}
}

func flushErrors() {
	if err := fetchError(); err != nil {
		panic(fmt.Sprintf("glfw: uncaught error: %s", err))
	}
}

func acceptError(codes ...ErrorCode) error {
	err := fetchError()
	if err == nil {
		return nil
	}
	for _, c := range codes {
		if err.(*glfwError).code == c {
			return nil
		}
	}
	if err.(*glfwError).code == PlatformError {
		// PlatformError is not handled here (See github.com/go-gl/glfw's implementation).
		// TODO: Should we log this error?
		return nil
	}
	return err
}

func goGLFWErrorCallback(code uintptr, desc *byte) uintptr {
	flushErrors()
	err := &glfwError{
		code: ErrorCode(code),
		desc: bytePtrToString(desc),
	}
	select {
	case lastErr <- err:
	default:
		panic(fmt.Sprintf("glfw: uncaught error: %s", err))
	}
	return 0
}

var glfwDLL *dll

func init() {
	dll, err := loadDLL()
	if err != nil {
		panic(err)
	}
	glfwDLL = dll

	glfwDLL.call("glfwSetErrorCallback", windows.NewCallbackCDecl(goGLFWErrorCallback))
}