clipToImageAlpha won't work on Windows

General JUCE discussion
1

I’m using clipToImageAlpha() in my plugin to ensure that user-supplied images are transparent in certain areas. It works like a charm on Mac, but on Windows the entire image becomes transparent instead.

Here is my code:

void makeHolesInImage(Image &image)
{
    Graphics g(image);
    auto &context = g.getInternalContext();
    context.clipToImageAlpha(clippingImage, AffineTransform());
    image.clear(image.getBounds(), Colour(0.0f, 0.0f, 0.0f, 0.0f));
}

Any ideas what I might be doing wrong? Or is it a problem with JUCE? This is on JUCE 6.1.4, by the way.

2

No takers? I guess I’ll just have to skip that feature, then.

3

Please don’t use the internal context (it’s internal for a reason). Simply use

juce::Graphics::reduceClipRegion ( const juce::Image& image, const juce::AffineTransform& transform )

It should do exactly what you want.

4

Thanks for the reply!

I tried your suggestion now, but unfortunately I get the exact same result: Works as expected on Mac, but on Windows the whole image becomes transparent.

Here’s the code, maybe I’m still using it wrong?

void makeHolesInImage(Image &image)
{
    Graphics g(image);
    g.reduceClipRegion(clippingImage, AffineTransform());
    image.clear(image.getBounds(), Colour(0.0f, 0.0f, 0.0f, 0.0f));
}
5

You don’t have to clear the source image, but instead draw the source image into the new graphics context.

6

I’m not sure I follow? Could you show me how I should modify the code I posted above to do that?

I tried replacing image.clear() with g.drawImage(), but that doesn’t seem to modify the image at all, so now the image is completely unchanged instead, and on both Mac and Windows.

7

OK. First, you will have to create a new bitmap, the same size as the bitmap you want to punch a hole into. It has to be cleared with black transparent alpha.

Then you create a graphics context with the new image as the target.

Then you reduce the clipping region with your clipping image.

Then you draw the customer’s image into the new bitmap.

8

Ah, yes, of course! I was still stuck on the idea of modifying the original image, sorry for being a bit dense…

Drawing into the new image worked perfectly! Thank you so much for helping me out with this!