Tk Source Code

To me, [df4b603950] seems like a combination of 2 issues. The primary issue was that TkScrollWindow() did not compute damage correctly when a widget was outside the visible portion of a toplevel, causing artifacts to appear. I think Marc's changes to TkScrollWindow() have fixed this.

I find the distortion in those artifacts to be a secondary issue, because if only the changes to TkScrollWindow() were made, then there would have been no more artifacts to notice.

I think there still exists a problem with CreateCGImageFromDrawableRect() where it can unexpectedly return a smaller image than requested. That led to the distorted scaling artifacts, but currently it can also lead to a buffer overread in XGetImage(). I want to say that the cause is that I neglected how CGImageCreateWithImageInRect() understandably does not “pad” the output image when specifying a rectangle extending outside of the input image. What I think CreateCGImageFromDrawableRect() should do instead is just always create a new bitmap context with the requested width and height, draw the image of the source drawable (pixmap or toplevel) at the correct offset into the new bitmap context (i.e. no need to obtain a subimage with CGImageCreateWithImageInRect()), then return the image from the new bitmap context. With this approach, there is nothing in XCopyArea() specifically to change from before; it continues to work with pixmaps and remains unaware of things like a toplevel's NSView. Here is the approach based on [b1b79d9302] (i.e. main branch from 5 months ago): https://github.com/chrstphrchvz/tk/commit/0bbbbc3c7e If there is interest in this, I can create a branch on Fossil.

Please see Fossil branch bug-df4b603950-alt

Hi Christopher.  I think this sounds very good.

> If there is interest in this, I can create a branch on Fossil.

Would you please be so kind as to do that?  Thanks.

The approach here also allows [de6ef8276c] to be fixed; I verified this by no longer defining TK_CAN_RENDER_RGBA in tkMacOSXPort.h.

Example script using TkImg to trigger a buffer overread in XGetImage() on a non-Retina display:

package require Tk
package require Img

. configure -width 200 -height 100 -background red
ttk::button .b -text "Capture this button                  " -command {do_capture .b}
place .b -x 20 -y 30

proc {do_capture} {w} {
	set capture_photo [image create photo -format window -data $w]
	toplevel .t$capture_photo
	pack [label .t$capture_photo.l -image $capture_photo]
}

The overread occurs on the line:

pixel32 pixel = *((pixel32 *)(bitmap + m));