Windows 上的 SKIA 渲染（来自 HDC 的 SkCanvas）

Question

我正在尝试使用 SKIA 在 Windows 上绘图。

有没有办法从HDC启动SkCanvas？

Answer 1

Windows 上有几种方法 "to use" skia。 skia 文件夹中 skia\src\views\win 的 SkOSWindow_win.cpp 中描述了这些方法。

例如：

您可以将 OpenGL 视口附加到您的 window，因为它已在函数 SkOSWindow::attachGL

中完成

HDC dc = GetDC((HWND)fHWND);
if (NULL == fHGLRC) {
    fHGLRC = SkCreateWGLContext(dc, msaaSampleCount,
        kGLPreferCompatibilityProfile_SkWGLContextRequest);
    if (NULL == fHGLRC) {
        return false;
    }
    glClearStencil(0);
    glClearColor(0, 0, 0, 0);
    glStencilMask(0xffffffff);
    glClear(GL_STENCIL_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
}
if (wglMakeCurrent(dc, (HGLRC)fHGLRC)) {
    // use DescribePixelFormat to get the stencil bit depth.
    int pixelFormat = GetPixelFormat(dc);
    PIXELFORMATDESCRIPTOR pfd;
    DescribePixelFormat(dc, pixelFormat, sizeof(pfd), &pfd);
    info->fStencilBits = pfd.cStencilBits;

    // Get sample count if the MSAA WGL extension is present
    SkWGLExtensions extensions;
    if (extensions.hasExtension(dc, "WGL_ARB_multisample")) {
        static const int kSampleCountAttr = SK_WGL_SAMPLES;
        extensions.getPixelFormatAttribiv(dc,
            pixelFormat,
            0,
            1,
            &kSampleCountAttr,
            &info->fSampleCount);
    }
    else {
        info->fSampleCount = 0;
    }

    glViewport(0, 0,
        SkScalarRoundToInt(this->width()),
        SkScalarRoundToInt(this->height()));
    return true;
}

您可以像在 SkOSWindow::doPaint 中所做的那样，通过执行 BitBlt 操作将 SkCanvas 的内容复制到 HDC

HDC hdc = (HDC)ctx;
const SkBitmap& bitmap = this->getBitmap();

BITMAPINFO bmi;
memset(&bmi, 0, sizeof(bmi));
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = bitmap.width();
bmi.bmiHeader.biHeight = -bitmap.height(); // top-down image
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;
bmi.bmiHeader.biSizeImage = 0;

//
// Do the SetDIBitsToDevice.
//
// TODO(wjmaclean):
//       Fix this call to handle SkBitmaps that have rowBytes != width,
//       i.e. may have padding at the end of lines. The SkASSERT below
//       may be ignored by builds, and the only obviously safe option
//       seems to be to copy the bitmap to a temporary (contiguous)
//       buffer before passing to SetDIBitsToDevice().
SkASSERT(bitmap.width() * bitmap.bytesPerPixel() == bitmap.rowBytes());
bitmap.lockPixels();
int ret = SetDIBitsToDevice(hdc,
    0, 0,
    bitmap.width(), bitmap.height(),
    0, 0,
    0, bitmap.height(),
    bitmap.getPixels(),
    &bmi,
    DIB_RGB_COLORS);
(void)ret; // we're ignoring potential failures for now.
bitmap.unlockPixels();

Windows 上的 SKIA 渲染（来自 HDC 的 SkCanvas）

SKIA Rendering on Windows(SkCanvas from HDC)

chromium

skia