gdiplus:GdipDrawImagePointsRect has a nosie vertical lineoutputafter resampled

[Liu Changhui]

Dear Vincent: 
The PixelFormat32bppRGB shuld be PixelFormat32bppARGB in the 
test_GdipDrawImagePointsRectNeedResample function of my patch.


In test_GdipDrawImagePointsRectNeedResample,  the first src_pointf valuse is :
X=5.992676, src_pointf.Y=0.000000 when the destination pixel is(x=699,y=0),
and srcx=6.000000,srcy=0.000000,srcwidth=48.000000,srcheight=26.000000,


so the follow if statement will test false :
if (src_pointf.X >= srcx && src_pointf.X < srcx + srcwidth && src_pointf.Y >= srcy && src_pointf.Y < srcy+srcheight)


then the destination pixel (x=699,y=0) will be filled with zero value,
but we expect that pixel shoule be filled a color same as the source image.


I think make these variables:
dst_to_src_points, src_pointf, x_dx, x_dy, y_dx, y_dy all use 64bit double float type maybe can fixed this situation. 
But GpointF and GpMatrix has used 32bit float type, and many gdiplus functions depended on them.


Can you give me some advice ? Thank you!

 
 
------------------ Original ------------------
From:  "Vincent Povirk"<madewokherd at gmail.com>;
Date:  Sun, Nov 23, 2014 12:57 PM
To:  "刘昌辉"<liuchanghui at linuxdeepin.com>; 
Cc:  "Sebastian Lackner"<sebastian at fds-team.de>; "wine-devel"<wine-devel at winehq.org>; 
Subject:  Re: gdiplus:GdipDrawImagePointsRect has a nosie vertical lineoutputafter resampled

 
This will cause us to draw outside of the destination when the image
is both enlarged and rotated.

That if statement is there to make sure we only draw to the area
inside the shape defined by the points array. src_pointf should be
within the range defined by srcx/srcy/srcwidth/srcheight if and only
if (x,y) is within that shape. If that's not the case, it probably
means we're calculating src_pointf incorrectly for the whole image,
not just the edges.

I'm not sure Sebastian realized this, but in this case
GdipBitmapGetPixel is different from reading the image directly.
Because PixelFormat32bppRGB does not store alpha data in the bitmap,
GdipBitmapGetPixel will always return an alpha value of 255, and you
will get a non-zero value even if the pixel is black. I suggest
testing for the exact value you expect. That should also remove the
need for the trace() calls.
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