在Android上绘制没有缩放的位图

Question

我试图在画布上绘制地图.在模拟器中,似乎图像模糊.android是否可能自动缩放位图？我确实尝试禁用缩放比如

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

模糊意味着如果我在位图中有一个像素,我看到像2x2像素.所以一个像素丢失了.所以我认为Android会自动缩放它以适应不同的屏幕.我只是使用WVGA,我该如何防止这种缩放？谢谢.

Answer 1

的确,Bitmap和Canvas具有密度特性,如果画在画布和位图的密度不同的位图将自动缩放位图.

从Bitmap.setDensity()文档:

指定此位图的密度.当位图绘制到也具有密度的Canvas时,它将被适当缩放.

您可以调用bitmap.setDensity(Bitmap.DENSITY_NONE)以完全禁用此自动缩放行为.如果从资源加载位图,将其置于其下drawable-nodpi就足够了.

对于好奇:这种行为背后的逻辑是在Canvas.cpp(本机部分android.graphics.Canvas),在drawBitmap__BitmapFFPaint()方法中实现的:

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();
    }
}