Question

我有一个Bitmap，我需要将其部分像素设置为透明。虽然我用Config.ARGB_8888创建了Bitmap，但当我在其上调用Bitmap.hasAlpha（）时，它返回false。我不能使用Bitmap.setHasAlpha（），因为它仅在API级别12中添加，而我的最低支持API需要为9.我该怎么做？

Answer 1

你走了：

Paint paint = new Paint();
paint.setAlpha(100);
canvas.drawBitmap(bitmap, src, dst, paint);

How to change a bitmap's opacity?

编辑：

//Create an array of pixels of the bitmap using Bitmap getPixels function
//Traverse through the pixels array and if that pixel matches your condition to change it to transparent
// Change the color of that pixel to transparent using Color.Transparent
//Finally set them back using Bitmap setPixels function

示例代码：

import android.graphics.Color;

int[] pixels = new int[myBitmap.getHeight()*myBitmap.getWidth()];
myBitmap.getPixels(pixels, 0, myBitmap.getWidth(), 0, 0, myBitmap.getWidth(),       myBitmap.getHeight());

//traverse through pixel array and if condition is met 
    pixels[i] = Color.TRANSPARENT;
myBitmap.setPixels(pixels, 0, myBitmap.getWidth(), 0, 0, myBitmap.getWidth(), myBitmap.getHeight());

how to change the color of certain pixels in bitmap android

Answer 2

// Convert red to transparent in a bitmap
public static Bitmap makeAlpha(Bitmap bit) {
    int width =  bit.getWidth();
    int height = bit.getHeight();
    Bitmap myBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    int [] allpixels = new int [ myBitmap.getHeight()*myBitmap.getWidth()];
    bit.getPixels(allpixels, 0, myBitmap.getWidth(), 0, 0, myBitmap.getWidth(),myBitmap.getHeight());
    myBitmap.setPixels(allpixels, 0, width, 0, 0, width, height);
            return myBitmap;
      }

上面的代码相当于setHasAlpha。给它一个位图，它将返回HasAlpha为真的位图，因此能够具有透明度。这适用于API级别8.我没有在低级别测试它。

如何设置位图pre-setHasAlpha的alpha？

2 个答案: