Thank you Mattias and Christian for your informations! I first think that TCanvas and TFPCanvas where much more related but this is not the case.
Using your informations I do the following patch for win32winapi.inc TWin32WidgetSet.StretchMaskBlt and this solve the problem! I think this solve the bug report 1907 and 6983. TFPCanvas.StretchDraw remain interesting in specific case, particulary if you want non pixelized zooming but I understand that speed is more important for the default function. Patrick
win32winapi.patch
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