Fix GC#drawImage + ImageGcDrawer for Cropping and Scaling #2913
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The GC#drawImage method takes (image, srcX, srcY, srcWidth, srcHeight, destX, destY, destWidth, destHeight) as arguments and crops and scales from the source region to the destination region. Passing an image drawn via ImageGCDrawer led to the following issue: The image handle from the subcall is resolved using the monitor zoom (data.nativeZoom) and the calculated scaledImageZoom (gcZoom * scaleFactor). This handle corresponds to an ImageData initialized at scaledImageZoom, whereas the drawings of the second GC are performed using the monitor zoom, subject to the auto-scale property. This mismatch results in unaligned sizing of drawings. For example, a 200% monitor zoom combined with a scale factor of 0.5 produces a scaledImageZoom of 100%. As a result, the ImageData is initialized at 100%, while drawing occurs at 200%. This exact case is demonstrated in vi-eclipse/Eclipse-Platform#554 . Furthermore, the calculation of scaledImageZoom uses fallback logic that only allows 100% and 200% as possible outcomes, which is clearly unintended in this context. The fix delegates resolving the correct handle to the Image class by passing the calculated scaledImageZoom. A callback then creates a new handle for this zoom, respecting the auto-scale property. If the returned handle matches the full image scaled to the requested scaledImageZoom in width and height, the source region coordinates/width/height are passed directly in pixels at that zoom. Otherwise, the internal zoom factor is derived from the returned handle’s width relative to the full image, and the source region coordinates are converted to pixel values using this internal zoom.
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The GC#drawImage method takes
(image, srcX, srcY, srcWidth, srcHeight, destX, destY, destWidth, destHeight) as arguments and crops and scales from the source region to the destination region.
Passing an image drawn via ImageGCDrawer led to the following issue:
The image handle from the subcall is resolved using the monitor zoom (data.nativeZoom) and the calculated scaledImageZoom (gcZoom * scaleFactor). This handle corresponds to an ImageData initialized at scaledImageZoom, whereas the drawings of the second GC are performed using the monitor zoom, subject to the auto-scale property.
This mismatch results in unaligned sizing of drawings. For example, a 200% monitor zoom combined with a scale factor of 0.5 produces a scaledImageZoom of 100%. As a result, the ImageData is initialized at 100%, while drawing occurs at 200%.
Furthermore, the calculation of scaledImageZoom uses fallback logic that only allows 100% and 200% as possible outcomes, which is clearly unintended in this context.
The fix delegates resolving the correct handle to the Image class by passing the calculated scaledImageZoom. A callback then creates a new handle for this zoom, respecting the auto-scale property.
If the returned handle matches the full image scaled to the requested scaledImageZoom in width and height, the source region coordinates/width/height are passed directly in pixels at that zoom. Otherwise, the internal zoom factor is derived from the returned handle’s width relative to the full image, and the source region coordinates are converted to pixel values using this internal zoom.
Note: Snippet 10 used to demonstrate that method. Although the sizing issue is fixed, the method is replaced by GC#drawImage(destX, destY, destWidth, destHeight) as the use case here is only scaling and not cropping. Currently, a new snippet is in progress which will be developed to address the cropping + scaling scenario (see #2912 as a first version without drawings via the ImageGcDrawer).