Create a standalone example for using Skia with SDL

example/SkiaSDLExample.cpp

Index: example/SkiaSDLExample.cpp
diff --git a/example/SkiaSDLExample.cpp b/example/SkiaSDLExample.cpp
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index 0000000000000000000000000000000000000000..5bd6aa08cd2d368e734c4872a2d91c0be2e18514
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+++ b/example/SkiaSDLExample.cpp
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+/*
+ * 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
+

[robertphillips, 2015/11/13 14:02:52]

// 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)

?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+struct ApplicationState {

[robertphillips, 2015/11/13 14:02:51]

// Storage for the user created rectangles. The last one may still be being
edited.

?

[joshualitt, 2015/11/13 18:51:56]

Acknowledged.

+    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) {

[robertphillips, 2015/11/13 14:02:51]

It might be clearer to make this "SkRect& rect ..." and then just update the
bottom & right slots

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+                    const SkRect& rect = state->fRects.back();
+                    state->fRects.back() = SkRect::MakeLTRB(rect.fLeft, rect.fTop,
+                                                            event.motion.x, 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;
+        }
+    }
+}
+

[robertphillips, 2015/11/13 14:02:51]

// Create a pentagram
?

maybe rename the function ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+static SkPath setup_concave_path() {

[robertphillips, 2015/11/13 14:02:52]

static const int kNumPoints = 5;

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SkPath concavePath;
+    SkPoint points[5] = {{0, SkIntToScalar(-50)} };
+    SkMatrix rot;
+    rot.setRotate(SkIntToScalar(360) / 5);
+    for (int i = 1; i < 5; ++i) {
+        rot.mapPoints(points + i, points + i - 1, 1);
+    }
+    concavePath.moveTo(points[0]);

[robertphillips, 2015/11/13 14:02:51]

shouldn't this loop start at 1 ?

[joshualitt, 2015/11/13 18:51:55]

dunno, it looks right.  Why rock the boat?  (Unless you have a strong opinion)

[robertphillips, 2015/11/13 19:02:59]

Don't we do a moveTo followed by a lineTo to the same point?

+    for (int i = 0; i < 5; ++i) {
+        concavePath.lineTo(points[(2 * i) % 5]);
+    }

[robertphillips, 2015/11/13 14:02:51]

concavePath.close() ?

[joshualitt, 2015/11/13 18:51:54]

Acknowledged.

+    concavePath.setFillType(SkPath::kEvenOdd_FillType);
+    SkASSERT(!concavePath.isConvex());
+    return concavePath;
+}
+
+/*
+ * In this example, we use Skia with SDL.
+ */
+#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_Window* window = nullptr;
+#if SK_SUPPORT_GPU
+    SDL_GLContext glContext = nullptr;
+#if defined(SK_BUILD_FOR_ANDROID)

[robertphillips, 2015/11/13 14:02:51]

Can we pull out the two shared lines ?

// For Android we need to set up for OpenGL ES and we make the window hi res &
full screen

?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
+    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
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);

[robertphillips, 2015/11/13 14:02:52]

// For all other clients we use the core profile and operate in a window

?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+
+    windowFlags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE;
+#endif

[robertphillips, 2015/11/13 14:02:51]

Why not 8 ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
+    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 5);
+    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
+    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);

[robertphillips, 2015/11/13 14:02:52]

Can we set depth to 0 ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);

[robertphillips, 2015/11/13 14:02:51]

// Skia needs 8 stencil bits

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
+
+    SDL_GL_SetAttribute(SDL_GL_ACCELERATED_VISUAL, 1);
+#endif // SK_SUPPORT_GPU
+

[robertphillips, 2015/11/13 14:02:51]

put this in the SK_SUPPORT_GPU block ?

where is msaaSampleCount coming from ?
should it be "static const int kMSAASampleCount = 0;" ?

[joshualitt, 2015/11/13 18:51:55]

I setup the static variable, but got rid of the SK_SUPPORT_GPU.  I'm not going
to bother trying to get this to work without GPU support

+    // If you want multisampling, uncomment the below lines
+    // SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
+    // SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, msaaSampleCount);
+
+    /*
+     * 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;
+    }
+

[robertphillips, 2015/11/13 14:02:51]

rm this ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SkDebugf("Desktop display mode is %dx%d\n", dm.w, dm.h);
+

[robertphillips, 2015/11/13 14:02:51]

Add "SDL_Window*" here and remove the above declaration ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    window = SDL_CreateWindow("Skia + 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());
+

[robertphillips, 2015/11/13 14:02:51]

uncomment this -> comment this out ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    // To use NVPR, uncomment this
+    interface.reset(GrGLInterfaceRemoveNVPR(interface));
+    SkASSERT(interface);
+
+    // setup contexts
+    SkAutoTUnref<GrContext> grContext(GrContext::Create(kOpenGL_GrBackend,
+                                                        (GrBackendContext)interface.get()));
+    SkASSERT(grContext);
+

[robertphillips, 2015/11/13 14:02:51]

// Wrap the frame buffer object attached to the screen in a Skia render target
so Skia can render to it

?

Should this be a subroutine - wrap_fbo_for_skia ?

[joshualitt, 2015/11/13 18:51:55]

Then its just a function which takes 10 arguments.  If this was production code
I would, but as an example its kind of nice to have all of the code in one
place.  If you have a strong preference I will change it.

+    // setup rendertarget
+    GrBackendRenderTargetDesc desc;
+    desc.fWidth = dm.w;
+    desc.fHeight = dm.h;
+    desc.fConfig = kSkia8888_GrPixelConfig;
+    desc.fOrigin = kBottomLeft_GrSurfaceOrigin;

[robertphillips, 2015/11/13 14:02:52]

kMSAASampleCount ?

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    desc.fSampleCnt = 0; // This would have to change for MSAA
+    desc.fStencilBits = 8;
+    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;
+    sk_bzero(&state, sizeof(ApplicationState));
+
+    const char* helpMessage = "Click and drag to create rects.  Press esc to quit.";
+
+    SkPaint paint;
+

[robertphillips, 2015/11/13 14:02:52]

Can this be  "SkImage* make_a_raster_image()"  ?

[joshualitt, 2015/11/13 18:51:55]

see my response to wrap_fbo_for_skia. 

+    // create a surface for CPU rasterization

[robertphillips, 2015/11/13 14:02:52]

offscreenInfo seem unused

[joshualitt, 2015/11/13 18:51:55]

Acknowledged.

+    SkImageInfo offscreenInfo = canvas->imageInfo();
+    offscreenInfo.makeWH(2000, 2000);

[robertphillips, 2015/11/13 14:02:51]

That's a big hunk o' memory
Can it just be the size of the concave path's bounding box ?

[joshualitt, 2015/11/13 18:51:54]

Acknowledged.

+    SkAutoTUnref<SkSurface> cpuSurface(SkSurface::NewRasterN32Premul(5000, 5000));
+
+    SkCanvas* offscreen = cpuSurface->getCanvas();
+    offscreen->save();
+    offscreen->translate(50.0f, 50.0f);
+    offscreen->drawPath(setup_concave_path(), 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;
+}