Create a standalone example for using Skia with SDL

example/SkiaSDLExample.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ */
+
+#include "GrContext.h"
+#include "SDL.h"
+#include "SkCanvas.h"
+#include "SkRandom.h"
+#include "SkSurface.h"
+
+#include "gl/GrGLInterface.h"
+#include "gl/GrGLUtil.h"
+
+#if defined(SK_BUILD_FOR_ANDROID)
+#include <GLES/gl.h>
+#elif defined(SK_BUILD_FOR_UNIX)
+#include <GL/gl.h>
+#elif defined(SK_BUILD_FOR_MAC)
+#include <gl.h>
+#endif
+
+/*
+ * This application is a simple example of how to combine SDL and Skia it demonstrates:
+ *   how to setup gpu rendering to the main window
+ *   how to perform cpu-side rendering and draw the result to the gpu-backed screen
+ *   draw simple primitives (rectangles)
+ *   draw more complex primitives (star)
+ */
+
+struct ApplicationState {
+    ApplicationState() : fQuit(false) {}
+    // Storage for the user created rectangles. The last one may still be being edited.
+    SkTArray<SkRect> fRects;
+    bool fQuit;
+};
+
+static void handle_error() {
+    const char* error = SDL_GetError();
+    SkDebugf("SDL Error: %s\n", error);
+    SDL_ClearError();
+}
+
+static void handle_events(ApplicationState* state, SkCanvas* canvas) {
+    SDL_Event event;
+    while(SDL_PollEvent(&event)) {
+        switch (event.type) {
+            case SDL_MOUSEMOTION:
+                if (event.motion.state == SDL_PRESSED) {
+                    SkRect& rect = state->fRects.back();
+                    rect.fRight = event.motion.x;
+                    rect.fBottom = event.motion.y;
+                }
+                break;
+            case SDL_MOUSEBUTTONDOWN:
+                if (event.button.state == SDL_PRESSED) {
+                    state->fRects.push_back() = SkRect::MakeLTRB(SkIntToScalar(event.button.x),
+                                                                 SkIntToScalar(event.button.y),
+                                                                 SkIntToScalar(event.button.x),
+                                                                 SkIntToScalar(event.button.y));
+                }
+                break;
+            case SDL_KEYDOWN: {
+                SDL_Keycode key = event.key.keysym.sym;
+                if (key == SDLK_ESCAPE) {
+                    state->fQuit = true;
+                }
+                break;
+            }
+            case SDL_QUIT:
+                state->fQuit = true;
+                break;
+            default:
+                break;
+        }
+    }
+}
+
+// Creates a star type shape using a SkPath
+static SkPath create_star() {
+    static const int kNumPoints = 5;
+    SkPath concavePath;
+    SkPoint points[kNumPoints] = {{0, SkIntToScalar(-50)} };
+    SkMatrix rot;
+    rot.setRotate(SkIntToScalar(360) / kNumPoints);
+    for (int i = 1; i < kNumPoints; ++i) {
+        rot.mapPoints(points + i, points + i - 1, 1);
+    }
+    concavePath.moveTo(points[0]);
+    for (int i = 0; i < kNumPoints; ++i) {
+        concavePath.lineTo(points[(2 * i) % kNumPoints]);
+    }
+    concavePath.setFillType(SkPath::kEvenOdd_FillType);
+    SkASSERT(!concavePath.isConvex());
+    concavePath.close();
+    return concavePath;
+}
+
+#if defined(SK_BUILD_FOR_ANDROID)
+int SDL_main(int argc, char** argv) {
+#else
+int main(int argc, char** argv) {
+#endif
+    uint32_t windowFlags = 0;
+
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+
+    SDL_GLContext glContext = nullptr;
+#if defined(SK_BUILD_FOR_ANDROID)
+    // For Android we need to set up for OpenGL ES and we make the window hi res & full screen
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
+    windowFlags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE |
+                  SDL_WINDOW_BORDERLESS | SDL_WINDOW_FULLSCREEN_DESKTOP |
+                  SDL_WINDOW_ALLOW_HIGHDPI;
+#else
+    // For all other clients we use the core profile and operate in a window
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+
+    windowFlags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE;
+#endif
+    static const int kStencilBits = 8;  // Skia needs 8 stencil bits
+    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
+    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, kStencilBits);
+
+    SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
+
+    // If you want multisampling, uncomment the below lines and set a sample count
+    static const int kMsaaSampleCount = 0; //4;
+    // SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
+    // SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, kMsaaSampleCount);
+
+    /*
+     * In a real application you might want to initialize more subsystems
+     */
+    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_EVENTS) != 0) {
+        handle_error();
+        return 1;
+    }
+
+    // Setup window
+    // This code will create a window with the same resolution as the user's desktop.
+    SDL_DisplayMode dm;
+    if (SDL_GetDesktopDisplayMode(0, &dm) != 0) {
+        handle_error();
+        return 1;
+    }
+
+    SDL_Window* window = SDL_CreateWindow("SDL Window", SDL_WINDOWPOS_CENTERED,
+                                          SDL_WINDOWPOS_CENTERED, dm.w, dm.h, windowFlags);
+
+    if (!window) {
+        handle_error();
+        return 1;
+    }
+
+    // To go fullscreen
+    // SDL_SetWindowFullscreen(window, SDL_WINDOW_FULLSCREEN);
+
+    // try and setup a GL context
+    glContext = SDL_GL_CreateContext(window);
+    if (!glContext) {
+        handle_error();
+        return 1;
+    }
+
+    int success =  SDL_GL_MakeCurrent(window, glContext);
+    if (success != 0) {
+        handle_error();
+        return success;
+    }
+
+    glViewport(0, 0, dm.w, dm.h);
+    glClearColor(1, 1, 1, 1);
+    glClearStencil(0);
+    glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
+
+    // setup GrContext
+    SkAutoTUnref<const GrGLInterface> interface(GrGLCreateNativeInterface());
+
+    // To use NVPR, comment this out
+    interface.reset(GrGLInterfaceRemoveNVPR(interface));
+    SkASSERT(interface);
+
+    // setup contexts
+    SkAutoTUnref<GrContext> grContext(GrContext::Create(kOpenGL_GrBackend,
+                                                        (GrBackendContext)interface.get()));
+    SkASSERT(grContext);
+
+    // Wrap the frame buffer object attached to the screen in a Skia render target so Skia can
+    // render to it
+    GrBackendRenderTargetDesc desc;
+    desc.fWidth = dm.w;
+    desc.fHeight = dm.h;
+    desc.fConfig = kSkia8888_GrPixelConfig;
+    desc.fOrigin = kBottomLeft_GrSurfaceOrigin;
+    desc.fSampleCnt = kMsaaSampleCount;
+    desc.fStencilBits = kStencilBits;
+    GrGLint buffer;
+    GR_GL_GetIntegerv(interface, GR_GL_FRAMEBUFFER_BINDING, &buffer);
+    desc.fRenderTargetHandle = buffer;
+    SkAutoTUnref<GrRenderTarget>
+            renderTarget(grContext->textureProvider()->wrapBackendRenderTarget(desc));
+
+    // setup SkSurface
+    // To use distance field text, use commented out SkSurfaceProps instead
+    // SkSurfaceProps props(SkSurfaceProps::kUseDeviceIndependentFonts_Flag,
+    //                      SkSurfaceProps::kLegacyFontHost_InitType);
+    SkSurfaceProps props(SkSurfaceProps::kLegacyFontHost_InitType);
+    SkAutoTUnref<SkSurface> surface(SkSurface::NewRenderTargetDirect(renderTarget, &props));
+
+    SkCanvas* canvas = surface->getCanvas();
+
+    ApplicationState state;
+
+    const char* helpMessage = "Click and drag to create rects.  Press esc to quit.";
+
+    SkPaint paint;
+
+    // create a surface for CPU rasterization
+    SkAutoTUnref<SkSurface> cpuSurface(SkSurface::NewRaster(canvas->imageInfo()));
+
+    SkCanvas* offscreen = cpuSurface->getCanvas();
+    offscreen->save();
+    offscreen->translate(50.0f, 50.0f);
+    offscreen->drawPath(create_star(), paint);
+    offscreen->restore();
+
+    SkAutoTUnref<SkImage> image(cpuSurface->newImageSnapshot());
+
+    int rotation = 0;
+    while (!state.fQuit) { // Our application loop
+        SkRandom rand;
+        canvas->clear(SK_ColorWHITE);
+        handle_events(&state, canvas);
+
+        paint.setColor(SK_ColorBLACK);
+        canvas->drawText(helpMessage, strlen(helpMessage), SkIntToScalar(100),
+                         SkIntToScalar(100), paint);
+        for (int i = 0; i < state.fRects.count(); i++) {
+            paint.setColor(rand.nextU() | 0x44808080);
+            canvas->drawRect(state.fRects[i], paint);
+        }
+
+        // draw offscreen canvas
+        canvas->save();
+        canvas->translate(dm.w / 2.0, dm.h / 2.0);
+        canvas->rotate(rotation++);
+        canvas->drawImage(image, -50.0f, -50.0f);
+        canvas->restore();
+
+        canvas->flush();
+        SDL_GL_SwapWindow(window);
+    }
+
+    if (glContext) {
+        SDL_GL_DeleteContext(glContext);
+    }
+
+    //Destroy window
+    SDL_DestroyWindow(window);
+
+    //Quit SDL subsystems
+    SDL_Quit();
+    return 0;
+}