Copy Image with its transformated Graphics context

General JUCE discussion
1

Hi there!

Is there a way I can create a copy of an Image maintaining the transformations I applied to its Graphics context?

For example:

auto image = Image(Image::ARGB, width, height, true);
Graphics context(image);
auto& internalContext = context.getInternalContext();
internalContext.addTransform(AffineTransformation::scale(2.0f));

auto newImage = image; // something to mantain internalContext transformation
Graphics newContext(newImage);
// newContext stuff...

Would Image::Image(const Image&) noexcept maintain this transformation?

Thank you!

2

Image is by default sharing the pixel data, so calling the copy constructor is just creating the Image with the same pixel data.

If you want a copy you need to call createCopy() or on the copy duplicateIfNeeded, which unlinks it from other images, that share the pixel data.

auto image = original.createCopy();
// or
juce::Image image (original);
image.duplicateIfNeeded();

For applying the transform you need to actually render it:

auto image = juce::Image (original.getFormat(), original.getWidth() * 2, original.getHeight() * 2, true);
juce::Graphics g (image);
g.drawImageTransformed (original, juce::AffineTransform::scale (2.0f));

And last but not least for this particular case there is a special function:

auto image = original.rescaled (original.getWidth() * 2, original.getHeight() * 2);

Hope that helps

3

Thank you for answering!

After some checks I realized that if a duplicate is made with createCopy() or duplicateIfShared() (and it’s shared) the transformations applied to the original image context are not maintained. If I use the copy constructor or the operator=() no duplicate is created (it just shares the pixel data, as you said) so these transformations are maintained. Shouldn’t the duplicates also maintain these transformations?

4

The transformations are handled and stored in the Graphics object, not the Image itself.
Think of the Graphics as a plotter, and the Image is the sheet of paper it is drawing onto.

1 Like
5

Thx, it worked!