internal/graphicsdriver/opengl/gl: use C version for Android

Unfortunately PureGo's dlopen didn't work on some Android devices.
Use the Cgo version instead in the same way as v2.7.

Closes #3052

internal/graphicsdriver/opengl/gl/default_cgo.go

@@ -2,7 +2,7 @@
 // SPDX-FileCopyrightText: 2014 Eric Woroshow
 // SPDX-FileCopyrightText: 2022 The Ebitengine Authors
 
-//go:build nintendosdk
+//go:build android || nintendosdk
 
 package gl
 

internal/graphicsdriver/opengl/gl/default_purego.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build (darwin || freebsd || linux || netbsd || openbsd || windows) && !nintendosdk && !playstation5
+//go:build (darwin || freebsd || (linux && !android) || netbsd || openbsd || windows) && !nintendosdk && !playstation5
 
 package gl
 

internal/graphicsdriver/opengl/gl/procaddr_android.go

@@ -0,0 +1,67 @@
+// Copyright 2024 The Ebitengine 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 gl
+
+// Unfortunately, PureGo's dlopen didn't work well on some Android devices (#3052).
+// Use Cgo instead until PureGo is fixed.
+
+// #include <dlfcn.h>
+// #include <stdlib.h>
+import "C"
+
+import (
+	"fmt"
+	"strings"
+	"unsafe"
+)
+
+var (
+	libGLES unsafe.Pointer
+)
+
+func (c *defaultContext) init() error {
+	// TODO: Use multiple %w-s as of Go 1.20.
+	var errors []string
+
+	// Try OpenGL ES.
+	for _, name := range []string{"libGLESv2.so", "libGLESv2.so.2", "libGLESv2.so.1", "libGLESv2.so.0"} {
+		cname := C.CString(name)
+		defer C.free(unsafe.Pointer(cname))
+		lib := C.dlopen(cname, C.RTLD_LAZY|C.RTLD_GLOBAL)
+		if lib != nil {
+			libGLES = lib
+			c.isES = true
+			return nil
+		}
+		if cerr := C.dlerror(); cerr != nil {
+			errors = append(errors, fmt.Sprintf("%s: %v", name, C.GoString(cerr)))
+		}
+	}
+
+	return fmt.Errorf("gl: failed to load libGLESv2.so: %s", strings.Join(errors, ", "))
+}
+
+func (c *defaultContext) getProcAddress(name string) (uintptr, error) {
+	cname := C.CString(name)
+	defer C.free(unsafe.Pointer(cname))
+	addr := C.dlsym(libGLES, cname)
+	if addr == nil {
+		if cerr := C.dlerror(); cerr != nil {
+			return 0, fmt.Errorf("gl: failed to load %s: %v", name, C.GoString(cerr))
+		}
+		return 0, fmt.Errorf("gl: failed to load %s", name)
+	}
+	return uintptr(addr), nil
+}

internal/graphicsdriver/opengl/gl/procaddr_linbsd.go

@@ -12,14 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build (freebsd || linux || netbsd || openbsd) && !nintendosdk && !playstation5
+//go:build (freebsd || (linux && !android) || netbsd || openbsd) && !nintendosdk && !playstation5
 
 package gl
 
 import (
 	"fmt"
 	"os"
-	"runtime"
 	"strings"
 
 	"github.com/ebitengine/purego"
@@ -32,16 +31,11 @@ var (
 
 func (c *defaultContext) init() error {
 	var preferES bool
-	if runtime.GOOS == "android" {
-		preferES = true
-	}
-	if !preferES {
-		for _, t := range strings.Split(os.Getenv("EBITENGINE_OPENGL"), ",") {
-			switch strings.TrimSpace(t) {
-			case "es":
-				preferES = true
-				break
-			}
+	for _, t := range strings.Split(os.Getenv("EBITENGINE_OPENGL"), ",") {
+		switch strings.TrimSpace(t) {
+		case "es":
+			preferES = true
+			break
 		}
 	}