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 <OpenGL/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
    sk_sp<const GrGLInterface> interface(GrGLCreateNativeInterface());

    // setup contexts
    sk_sp<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;

    // 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);

    sk_sp<SkSurface> surface(SkSurface::MakeFromBackendRenderTarget(grContext, desc, &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
    sk_sp<SkSurface> cpuSurface(SkSurface::MakeRaster(canvas->imageInfo()));

    SkCanvas* offscreen = cpuSurface->getCanvas();
    offscreen->save();
    offscreen->translate(50.0f, 50.0f);
    offscreen->drawPath(create_star(), paint);
    offscreen->restore();

    sk_sp<SkImage> image = cpuSurface->makeImageSnapshot();

    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;
}