android - 在 Android 上不缩放绘制位图

Question

我试图在 Canvas 上绘制位图。在模拟器中，图像似乎很模糊。 android可能会自动缩放位图吗？我确实尝试禁用缩放，例如

< supports-screens android:smallScreens="false" android:normalScreens="true" 
android:largeScreens="false" android:xlargeScreens="false" android:anyDensity="true" />

blur 意味着如果我在位图中有一个像素，我看到的是 2x2 像素。有时会丢失一个像素。所以我假设 Android 会自动缩放它以适应不同的屏幕。我只是使用 WVGA，如何防止这种缩放？谢谢。

Answer 1

事实上，Bitmap 和 Canvas 都有密度属性，如果 Canvas 和位图的密度不同，绘制位图会自动缩放位图。

来自 Bitmap.setDensity()文档:

Specifies the density for this bitmap. When the bitmap is drawn to a Canvas that also has a density, it will be scaled appropriately.

您可以调用 bitmap.setDensity(Bitmap.DENSITY_NONE) 来完全禁用这种自动缩放行为。如果您从资源中加载位图，将其放在 drawable-nodpi 下就足够了。

出于好奇:此行为背后的逻辑在 Canvas.cpp(android.graphics.Canvas 的 native 部分)中实现，在 drawBitmap__BitmapFFPaint () 方法:

static void drawBitmap__BitmapFFPaint(JNIEnv* env, jobject jcanvas,
                                      SkCanvas* canvas, SkBitmap* bitmap,
                                      jfloat left, jfloat top,
                                      SkPaint* paint, jint canvasDensity,
                                      jint screenDensity, jint bitmapDensity) {
    SkScalar left_ = SkFloatToScalar(left);
    SkScalar top_ = SkFloatToScalar(top);

    if (canvasDensity == bitmapDensity || canvasDensity == 0
            || bitmapDensity == 0) {
        if (screenDensity != 0 && screenDensity != bitmapDensity) {
            SkPaint filteredPaint;
            if (paint) {
                filteredPaint = *paint;
            }
            filteredPaint.setFilterBitmap(true);
            canvas->drawBitmap(*bitmap, left_, top_, &filteredPaint);
        } else {
            canvas->drawBitmap(*bitmap, left_, top_, paint);
        }
    } else {
        canvas->save();
        SkScalar scale = SkFloatToScalar(canvasDensity / (float)bitmapDensity);
        canvas->translate(left_, top_);
        canvas->scale(scale, scale);

        SkPaint filteredPaint;
        if (paint) {
            filteredPaint = *paint;
        }
        filteredPaint.setFilterBitmap(true);

        canvas->drawBitmap(*bitmap, 0, 0, &filteredPaint);

        canvas->restore();
    }
}