#79 Add TDC::GradientFill and TDC::AlphaBlend

[Vidar Hasfjord]

The Win32 bitmap functions GradientFill and AlphaBlend were introduced in Windows 98 (msimg32.lib), and thus there is no TDC counterpart in OWL. But now that these functions are available on all supported platforms (XP and later), they should be supported in TDC as well.

Note that the related function TDC::TransparentBlt was added in [r1306]. See [feature-requests:#50]. This ticket would complete the set of Win32 Bitmap Functions, as discussed in post "TResId + TransparentBlt in v6.30.11" in the Open Discussion forum.

GradientFill and AlphaBlend were implemented on the trunk in [r5024], with accompanying convenience functions GradientTriangleFill and GradientRectFill.

[Ognyan Chernokozhev]

Minor issue in [r5024] that the implementations of SetPixelV and AlphaBlent were missing the inline specification, and building of the OCFNext and other libraries was failing with linker errors. Fixed in [r5027].

[Ognyan Chernokozhev]

I tried the new GradientTriangleFill and GradientRectFill methods, as in the provided Doxygen examples, but both fail to compile with an error "Element type must be TRIVERTEX"

I added a TDC example to the Classes project - feel free to modify it and add to it.

[Vidar Hasfjord]

Hi Jogy, great of you to add an example for testing. Good catch on the documentation bug. It is an example of slicing, and the code error catches it. The array must be of type TRIVERTEX, not a derived type, for it to be passed to the Windows API.

I have updated the documentation and the example [r5041].

Edit: Simplification of the example, using initializer lists, in [r5042].