Make button glyphs have transparent background in delphi 7?
I have four TSpeedButton objects, each with a BMP file assigned as a symbol for the button image. For some reason, delphi decided that two button images should have a transparent background and two should have a white background. I created the bitmaps myself, so they are all kept at the same color depth and use a white background (not some shade of almost white) for the background and have a background color in all four corner pixels of the image.
Why do some of the glyph images appear with a transparent background and some do not? What is the criterion for background transparency? How can I make my button images have transparent backgrounds instead of half of them having transparent backgrounds?
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Delphi's glyph processing uses the pixel in the lower left corner to define the transparent color. All pixels corresponding to this color should be shown as transparent. Is the bottom-left pixel color consistent across all glyphs and matches the areas you want to be transparent? (Without images, it's hard to tell what the problem is, but I thought I'd post this as an opportunity for research.)
the correct answer appeared (sorry, I cannot accept the comment as the correct answer!). The image I used had a drop shadow reaching the bottom left corner, so it was almost white in that corner and even white in all other corners.
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I had a similar problem with D5 and included a fix for this since I didn't find out why this was happening.
Set the image size to be equal to the Row above the actual image / glyph. This will cause the image to write from the top-left position and stop before the last line. This will force the use of an opaque color, and the extra line below the image will not be visually noticeable.
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