Android13 Canvas drawImage流程分析

Canvas的drawImage()方法是用于在画布上绘制图像的方法。它可以绘制图像、视频的某一帧图像以及其他画布的内容。此外，还可以对绘制的图像进行裁剪，代码如下：

//frameworks/base/graphics/java/android/graphic/Canvas.java
public class Canvas extends BaseCanvas {
    public void drawImage(Image image, float x, float y, SamplingOptions sampling) {
        nDrawImage(mNativeInstance, image.getNativeInstance(), x, y,
                   sampling.getNativeDesc(), sampling.getCubicCoeffB(), sampling.getCubicCoeffC());
    }
}

调用nDrawImage方法，该方法是一个Native方法，在Canvas.cpp中定义，通过查调用的是Canvas_DrawImage方法：

//external/skia/modules/androidkit/src/Canvas.cpp
void Canvas_DrawImage(JNIEnv* env, jobject, jlong native_instance, jlong native_image,
                      jfloat x, jfloat y,
                      jint sampling_desc, jfloat sampling_b, jfloat sampling_c) {
    auto* canvas = reinterpret_cast<SkCanvas*>(native_instance);
    auto*  image = reinterpret_cast<SkImage *>(native_image);


    if (canvas && image) {
        canvas->drawImage(image, x, y,
            androidkit::utils::SamplingOptions(sampling_desc, sampling_b, sampling_c));
    }
}

SkCanvas drawImage

调用SkCanvas的drawImage方法：

//external/skia/src/core/SkiaCanvas.cpp
class SK_API SkCanvas {
void SkCanvas::drawImage(const SkImage* image, SkScalar x, SkScalar y,
                         const SkSamplingOptions& sampling, const SkPaint* paint) {
    TRACE_EVENT0("skia", TRACE_FUNC);
    RETURN_ON_NULL(image);
    this->onDrawImage2(image, x, y, sampling, paint);
}

调用SkCanvas的onDrawImage2方法：

//external/skia/include/core/SkCanvas.cpp
class SK_API SkCanvas {
void SkCanvas::onDrawImage2(const SkImage* image, SkScalar x, SkScalar y,
                            const SkSamplingOptions& sampling, const SkPaint* paint) {
    SkPaint realPaint = clean_paint_for_drawImage(paint);


    SkRect bounds = SkRect::MakeXYWH(x, y, image->width(), image->height());
    if (this->internalQuickReject(bounds, realPaint)) {
        return;
    }


    if (realPaint.getImageFilter() &&
        this->canDrawBitmapAsSprite(x, y, image->width(), image->height(), sampling, realPaint) &&
        !image_to_color_filter(&realPaint)) {
        // Evaluate the image filter directly on the input image and then draw the result, instead
        // of first drawing the image to a temporary layer and filtering.
        SkBaseDevice* device = this->topDevice();
        sk_sp<SkSpecialImage> special;
        if ((special = device->makeSpecial(image))) {
            sk_sp<SkImageFilter> filter = realPaint.refImageFilter();
            realPaint.setImageFilter(nullptr);


            // TODO(michaelludwig) - Many filters could probably be evaluated like this even if the
            // CTM is not translate-only; the post-transformation of the filtered image by the CTM
            // will probably look just as good and not require an extra layer.
            // TODO(michaelludwig) - Once image filter implementations can support source images
            // with non-(0,0) origins, we can just mark the origin as (x,y) instead of doing a
            // pre-concat here.
            SkMatrix layerToDevice = device->localToDevice();
            layerToDevice.preTranslate(x, y);


            SkMatrix deviceToLayer;
            if (!layerToDevice.invert(&deviceToLayer)) {
                return; // bad ctm, d