Implement OpenGL backend in Android viewer app

tools/viewer/sk_app/android/GLWindowContext_android.cpp

Index: tools/viewer/sk_app/android/GLWindowContext_android.cpp
diff --git a/tools/viewer/sk_app/android/GLWindowContext_android.cpp b/tools/viewer/sk_app/android/GLWindowContext_android.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..a98b5553f848c9206e1f11fbfd8f13e329819b15
--- /dev/null
+++ b/tools/viewer/sk_app/android/GLWindowContext_android.cpp
@@ -0,0 +1,122 @@
+
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <GLES/gl.h> 
+
+#include "GLWindowContext_android.h"
+
+#include <android/native_window_jni.h>
+
+namespace sk_app {
+
+// Most of the following 3 functions (GLWindowContext::Create, constructor, desctructor)
+// are copied from Unix/Win platform with unix/win changed to android
+
+// platform-dependent create
+GLWindowContext* GLWindowContext::Create(void* platformData, const DisplayParams& params) {
+    GLWindowContext_android* ctx = new GLWindowContext_android(platformData, params);
+    if (!ctx->isValid()) {
+        delete ctx;
+        return nullptr;
+    }
+    return ctx;
+}
+
+GLWindowContext_android::GLWindowContext_android(void* platformData, const DisplayParams& params)
+    : GLWindowContext(platformData, params)
+    , fDisplay(EGL_NO_DISPLAY)
+    , fEGLContext(EGL_NO_CONTEXT)
+    , fSurface(EGL_NO_SURFACE) {
+
+    // any config code here (particularly for msaa)?
+
+    this->initializeContext(platformData, params);
+}
+
+GLWindowContext_android::~GLWindowContext_android() {
+    this->destroyContext();
+}
+
+void GLWindowContext_android::onInitializeContext(void* platformData, const DisplayParams& params) {
+    ContextPlatformData_android* androidPlatformData = 
+            reinterpret_cast<ContextPlatformData_android*>(platformData);
+
+    fWidth = ANativeWindow_getWidth(androidPlatformData->fNativeWindow);
+    fHeight = ANativeWindow_getHeight(androidPlatformData->fNativeWindow);
+
+    fDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);
+
+    EGLint majorVersion;
+    EGLint minorVersion;
+    eglInitialize(fDisplay, &majorVersion, &minorVersion);
+
+    SkAssertResult(eglBindAPI(EGL_OPENGL_ES_API));
+
+    EGLint numConfigs = 0;
+    const EGLint configAttribs[] = {
+        EGL_SURFACE_TYPE, EGL_PBUFFER_BIT,
+        EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
+        EGL_RED_SIZE, 8,
+        EGL_GREEN_SIZE, 8,
+        EGL_BLUE_SIZE, 8,
+        EGL_ALPHA_SIZE, 8,
+        EGL_NONE
+    };
+
+    EGLConfig surfaceConfig;
+    SkAssertResult(eglChooseConfig(fDisplay, configAttribs, &surfaceConfig, 1, &numConfigs));
+    SkASSERT(numConfigs > 0);
+
+    static const EGLint kEGLContextAttribsForOpenGLES[] = {
+        EGL_CONTEXT_CLIENT_VERSION, 2,
+        EGL_NONE
+    };
+    fEGLContext = eglCreateContext(
+            fDisplay, surfaceConfig, nullptr, kEGLContextAttribsForOpenGLES);
+    SkASSERT(EGL_NO_CONTEXT != fEGLContext);
+
+    fSurface = eglCreateWindowSurface(
+            fDisplay, surfaceConfig, androidPlatformData->fNativeWindow, nullptr);
+    SkASSERT(EGL_NO_SURFACE != fSurface);
+
+    SkAssertResult(eglMakeCurrent(fDisplay, fSurface, fSurface, fEGLContext));
+    // GLWindowContext::initializeContext will call GrGLCreateNativeInterface so we
+    // won't call it here.
+
+    glClearStencil(0);
+    glClearColor(0, 0, 0, 0);
+    glStencilMask(0xffffffff);
+    glClear(GL_STENCIL_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
+
+    int redBits, greenBits, blueBits;
+    eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_RED_SIZE, &redBits);
+    eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_GREEN_SIZE, &greenBits);
+    eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_BLUE_SIZE, &blueBits);
+    fColorBits = redBits + greenBits + blueBits;
+    eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_STENCIL_SIZE, &fStencilBits);
+    eglGetConfigAttrib(fDisplay, surfaceConfig, EGL_SAMPLES, &fSampleCount);
+}
+
+void GLWindowContext_android::onDestroyContext() {
+    if (!fDisplay || !fEGLContext || !fSurface) {
+        return;
+    }
+    eglMakeCurrent(fDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
+    SkAssertResult(eglDestroySurface(fDisplay, fSurface));
+    SkAssertResult(eglDestroyContext(fDisplay, fEGLContext));
+    fEGLContext = EGL_NO_CONTEXT;
+    fSurface = EGL_NO_SURFACE;
+}
+
+void GLWindowContext_android::onSwapBuffers() {
+    if (fDisplay && fEGLContext && fSurface) {
+        eglSwapBuffers(fDisplay, fSurface);
+    }
+}
+
+}