Format32bppRgb is acutally Format32bppRgba on Gtk

[nrother]

Expected Behavior

A Bitmap created with PixelFormat.Format32bppRgb and filled with 0x00FFFFFF should be all-white.

Actual Behavior

The Bitmap is completely transparent when shown in an ImageView on Gtk3. The documentation states 32-bits (4 bytes) per pixel, ordered by an Empty byte in the highest order, followed by Red, Green, and Blue., but actually the highest order byte is the alpha byte and not ignored.

Steps to Reproduce the Problem

see code

Code that Demonstrates the Problem

int[] pixelData = values.AsParallel().Select(x => {
    return (int)0x00FFFFFF; //broken
    //unchecked { return (int)0xFFFFFFFF; } //works
}).ToArray();

//create bitmap
var bitmap = new Bitmap(samplesPerLine, lines, PixelFormat.Format32bppRgb);

//copy data
using(var bitmapData = bitmap.Lock()) {
    IntPtr ptr = bitmapData.Data;
    GCHandle pixelHandle = GCHandle.Alloc(pixelData, GCHandleType.Pinned);
    for (int line = 0; line < lines; line++)
    {
        Marshal.Copy(pixelData, line * samplesPerLine, ptr, samplesPerLine);
        ptr += bitmapData.ScanWidth;
    }
}

Specifications

• Version: 2.4.1
• Platform(s): Gtk3
• Operating System(s): Ubuntu 18.04

[cwensley]

Hey @nrother, thanks for reporting the issue. Have you tried Eto 2.5?

[nrother]

Yes, this is the same in 2.5.0-rc.4

[cwensley]

Thanks for checking, @nrother.

[cwensley]

Fix is incoming. Note that Gtk/Cairo doesn't actually support 32bpp while ignoring alpha, so Eto now updates the alpha when necessary so that it shows it correctly. Using PixelFormats.Format32bppRgba is currently the most optimal format to use on all platforms.