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.
 *
 */

/*
 * Known to work with SDL2 2.30.11 and mis-behave with sdl2 compat 2.32.54 (on SDL3 3.2.10). HTL 2025-04-29
 *
 * Changes from chrome/m92:example/SkiaSDLExample.cpp - HTL 2024:
 *     - Update to current skia (m132+)
 *     - Default typeface has no visible glyph from m120/m121 onwards; must be initialized
 *     - Fix element-positioning bug due to window resizing:
 *         - The (*bottom*-left corner of) text is drawn 100,100 from *top*-left
 *         - Gnome-Shell forces the SDL window to resize to fit, as it tries to expand to fill full-screen
 *         - Therefore element positioning was off by about 105 pixels, which means the text is invisible,
 *           and the rects are drawn by a (variable) vertical offset from the mouse clicks.
 *
 * The python / GLFW c++ version goes further cosmetically: the (*top*-left of) text is exactly at 0,0 *top*-left,
 * and also centers the rotating star. This c++ code is quite inconsistent in drawing
 * the star fixed relative to the *bottom*-left corner, and the (*bottom*-left of) text relative to the
 * *top*-left.
 */

#include "include/gpu/ganesh/GrBackendSurface.h"
#include "include/gpu/ganesh/GrDirectContext.h"
#include "SDL.h"
#include "include/core/SkCanvas.h"
#include "include/core/SkFont.h"
#include "include/core/SkSurface.h"
#include "src/base/SkRandom.h"
#include "include/private/base/SkTArray.h"

#include "include/gpu/ganesh/gl/GrGLInterface.h"
#include "src/gpu/ganesh/gl/GrGLUtil.h"
#include "include/gpu/ganesh/SkSurfaceGanesh.h"
#include "include/gpu/ganesh/gl/GrGLDirectContext.h"
#include "include/gpu/ganesh/gl/GrGLBackendSurface.h"
#include "include/core/SkColorSpace.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>
#elif defined(SK_BUILD_FOR_IOS)
#include <OpenGLES/ES2/gl.h>
#endif
#include "include/core/SkFontMgr.h"
#ifdef __linux__
#include "include/ports/SkFontConfigInterface.h"
#include "include/ports/SkFontMgr_FontConfigInterface.h"
#endif
#ifdef __APPLE__
#include "include/ports/SkFontMgr_mac_ct.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.
    skia_private::TArray<SkRect> fRects;
    int window_width;
    int window_height;
    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_WINDOWEVENT:
                if(event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED ||
                   event.window.event == SDL_WINDOWEVENT_RESIZED) {
                   state->window_width  = event.window.data1;
                   state->window_height = event.window.data2;
                }
                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(SkPathFillType::kEvenOdd);
    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) || defined(SK_BUILD_FOR_IOS)
    // For Android/iOS 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;
    }

    uint32_t windowFormat = SDL_GetWindowPixelFormat(window);
    int contextType;
    SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &contextType);


    int dw, dh;
    SDL_GL_GetDrawableSize(window, &dw, &dh);

    glViewport(0, 0, dw, dh);
    glClearColor(1, 1, 1, 1);
    glClearStencil(0);
    glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

    // setup GrContext
    auto interface = GrGLMakeNativeInterface();

    // setup contexts
    sk_sp<GrDirectContext> grContext(GrDirectContexts::MakeGL(interface));
    SkASSERT(grContext);

    // Wrap the frame buffer object attached to the screen in a Skia render target so Skia can
    // render to it
    GrGLint buffer;
    GR_GL_GetIntegerv(interface.get(), GR_GL_FRAMEBUFFER_BINDING, &buffer);
    GrGLFramebufferInfo info;
    info.fFBOID = (GrGLuint) buffer;
    SkColorType colorType;

    //SkDebugf("%s", SDL_GetPixelFormatName(windowFormat));
    // TODO: the windowFormat is never any of these?
    if (SDL_PIXELFORMAT_RGBA8888 == windowFormat) {
        info.fFormat = GR_GL_RGBA8;
        colorType = kRGBA_8888_SkColorType;
    } else {
        colorType = kBGRA_8888_SkColorType;
        if (SDL_GL_CONTEXT_PROFILE_ES == contextType) {
            info.fFormat = GR_GL_BGRA8;
        } else {
            // We assume the internal format is RGBA8 on desktop GL
            info.fFormat = GR_GL_RGBA8;
        }
    }

    GrBackendRenderTarget target = GrBackendRenderTargets::MakeGL(dw, dh, kMsaaSampleCount, kStencilBits, info);

    // setup SkSurface
    // To use distance field text, use commented out SkSurfaceProps instead
    // SkSurfaceProps props(SkSurfaceProps::kUseDeviceIndependentFonts_Flag,
    //                      SkSurfaceProps::kUnknown_SkPixelGeometry);
    SkSurfaceProps props;

    sk_sp<SkSurface> surface(SkSurfaces::WrapBackendRenderTarget(grContext.get(), target,
                                                                    kBottomLeft_GrSurfaceOrigin,
                                                                    colorType, nullptr, &props));

    SkCanvas* canvas = surface->getCanvas();
    canvas->scale((float)dw/dm.w, (float)dh/dm.h);

    ApplicationState state;
    state.window_width  = dw;
    state.window_height = dh;

    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(SkSurfaces::Raster(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;
#ifdef __linux__
    sk_sp<SkFontConfigInterface> fc(SkFontConfigInterface::RefGlobal());
    sk_sp<SkTypeface> typeface(SkFontMgr_New_FCI(std::move(fc))->legacyMakeTypeface("",SkFontStyle()));
#endif
#ifdef __APPLE__
    sk_sp<SkTypeface> typeface(SkFontMgr_New_CoreText(nullptr)->legacyMakeTypeface("",SkFontStyle()));
#endif
    SkFont font(typeface);
    while (!state.fQuit) { // Our application loop
        SkRandom rand;
        canvas->clear(SK_ColorWHITE);
        handle_events(&state, canvas);

        paint.setColor(SK_ColorBLACK);
        canvas->translate(0, dh - state.window_height);
        canvas->drawString(helpMessage, 100.0f, 100.0f, font, paint);
        for (int i = 0; i < state.fRects.size(); i++) {
            paint.setColor(rand.nextU() | 0x44808080);
            canvas->drawRect(state.fRects[i], paint);
        }
        canvas->translate(0, -(dh - state.window_height));

        // 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();

        if (auto dContext = GrAsDirectContext(canvas->recordingContext())) {
            dContext->flushAndSubmit();
        }
        SDL_GL_SwapWindow(window);
    }

    if (glContext) {
        SDL_GL_DeleteContext(glContext);
    }

    //Destroy window
    SDL_DestroyWindow(window);

    //Quit SDL subsystems
    SDL_Quit();
    return 0;
}