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[GTK] Fix scaling of image copies and stylings #2653

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[GTK] Fix scaling of image copies and stylings #2653

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22 changes: 11 additions & 11 deletions bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/Image.java
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Original file line number Diff line number Diff line change
Expand Up @@ -278,16 +278,16 @@ public Image(Device device, Image srcImage, int flag) {
if (flag != SWT.IMAGE_DISABLE) transparentPixel = srcImage.transparentPixel;

long imageSurface = srcImage.surface;
int width = this.width = srcImage.width;
int height = this.height = srcImage.height;
this.width = srcImage.width;
this.height = srcImage.height;
int format = Cairo.cairo_surface_get_content(imageSurface) == Cairo.CAIRO_CONTENT_COLOR ? Cairo.CAIRO_FORMAT_RGB24 : Cairo.CAIRO_FORMAT_ARGB32;
boolean hasAlpha = format == Cairo.CAIRO_FORMAT_ARGB32;
surface = Cairo.cairo_image_surface_create(format, width, height);
int dataWidth = DPIUtil.pointToPixel(this.width, DPIUtil.getDeviceZoom());
int dataHeight= DPIUtil.pointToPixel(this.height, DPIUtil.getDeviceZoom());
surface = Cairo.cairo_image_surface_create(format, dataWidth, dataHeight);
if (surface == 0) SWT.error(SWT.ERROR_NO_HANDLES);
if (DPIUtil.getDeviceZoom() != currentDeviceZoom) {
double scaleFactor = DPIUtil.getDeviceZoom() / 100f;
Cairo.cairo_surface_set_device_scale(surface, scaleFactor, scaleFactor);
}
double scaleFactor = DPIUtil.getDeviceZoom() / 100f;
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Suggested change
double scaleFactor = DPIUtil.getDeviceZoom() / 100f;
double[] scaleX = new double[1];
double[] scaleY = new double[1];
Cairo.cairo_surface_get_device_scale(imageSurface, scaleX, scaleY);

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@akurtakov akurtakov Oct 24, 2025 •
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As this is copy of the image it's best to fetch the scale (cairo gives separate x/y scale factors) of the image copied.

Cairo.cairo_surface_set_device_scale(surface, scaleFactor, scaleFactor);
Comment on lines +289 to +290
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@akoch-yatta akoch-yatta Oct 21, 2025 •
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Is setting the scale still necessary? I don't get what the purpose is when the surface already has the correct size.

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Yes, it is necessary. Otherwise it will look like this:
image

In my understanding, you need to do two things (which are the two places I adapted):

  1. Give the correct size in pixels to the surface; by now we used the size in points, which led to have the expected size at 200% zoom
  2. Tell Cairo at what scale that surface is used to ensure that coordinates are properly transformed; this is basically the same we have to do in SWT with point/pixel conversion. If you leave that out, you have a surface of double the size (when device zoom is 200) but since you treat all coordinates as 100%, it will paint at half scale to the top-left area of the surface.

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@arunjose696 arunjose696 Oct 21, 2025 •
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I am still not able to understand a slight detail on how the images were drawn fully (although blurrily scaled) before, as the height and width of the surface was in points I would expect to the surface to have only data in half width and height or the image to be partially cut off, when the zoom is 200%

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That's because the surface scale was usually set to 1 as currentDeviceZoom and DPIUtil.getDeviceZoom() were equal. I don't know why the check was there at all.

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Suggested change
Cairo.cairo_surface_set_device_scale(surface, scaleFactor, scaleFactor);
Cairo.cairo_surface_set_device_scale(surface, scaleX[0], scaleY[0]);

long cairo = Cairo.cairo_create(surface);
if (cairo == 0) SWT.error(SWT.ERROR_NO_HANDLES);
Cairo.cairo_set_operator(cairo, Cairo.CAIRO_OPERATOR_SOURCE);
Expand All @@ -306,9 +306,9 @@ public Image(Device device, Image srcImage, int flag) {
switch (flag) {
case SWT.IMAGE_DISABLE: {
byte[] line = new byte[stride];
for (int y=0; y<height; y++) {
for (int y=0; y<dataHeight; y++) {
C.memmove(line, data + (y * stride), stride);
for (int x = 0, offset = 0; x < width; x++, offset += 4) {
for (int x = 0, offset = 0; x < dataWidth; x++, offset += 4) {
int a = line[offset + oa] & 0xFF;
int r = line[offset + or] & 0xFF;
int g = line[offset + og] & 0xFF;
Expand Down Expand Up @@ -339,9 +339,9 @@ public Image(Device device, Image srcImage, int flag) {
}
case SWT.IMAGE_GRAY: {
byte[] line = new byte[stride];
for (int y=0; y<height; y++) {
for (int y=0; y<dataHeight; y++) {
C.memmove(line, data + (y * stride), stride);
for (int x=0, offset = 0; x<width; x++, offset += 4) {
for (int x=0, offset = 0; x<dataWidth; x++, offset += 4) {
int a = line[offset + oa] & 0xFF;
int r = line[offset + or] & 0xFF;
int g = line[offset + og] & 0xFF;
Expand Down
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