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Stretching alpha-bitmaps

Submitted on: 2/11/2015 11:04:00 PM
By: Carles P.V. (from psc cd)  
Level: Intermediate
User Rating: By 28 Users
Compatibility: VB 6.0
Views: 2484
     Some additions: AlphaBltStrecth and AlphaBlendStretch with and without interpolation (bilinear). Thanks to Ron van Tilburg for the fast 'integer maths' version of Peter Scale's 'Bilinear resizing' routine. And about this, a note: API AlphaBlend stretches using nearest-neighbour method (it only allows COLORONCOLOR for SetStretchBltMode function). This has a simple explanation: interpolation of alpha-bitmaps involves "pre-blending" (composition) alpha-pixels before rendering onto given DC. This complicates processing. This is supposed what GDI+ solves. Attached, there is a GDI+ test project for comparison purposes (compare flower contour-pixels of both tests; increase iterations for better appreciation and use AlphaBlendStretch function). __________________________________________________ Update #1. Some effects; packed in mDIB32Ext module: 'ConvertToGrey', 'BlendWithColor' and 'ChangeGlobalAlpha'. You can add your own ones. Remember pixel data is stored as ARGB (BGRA byte array).

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