[lazarus] Bitmap transparency?

[Micha Nelissen]

Micha Nelissen wrote:

> Mattias Gaertner wrote:
> 
>>
>> Sounds like what we want. With the information in the RawImage 
>> description
>> the data created already matches the color format. The interface only 
>> needs
>> to setup the header.
>> The idea is to implement "CreateCompatibleBitmap" in a platform 
>> independent
>> way.
>> Under win32 afaik you would normally use CreateCompatibleBitmap to 
>> create a
>> bitmap. 
> 
> 
> The 'compatible' in CreateCompatibleBitmap means compatible to some DC. 
> With the current 5 fpimage functions, this function cannot be used, 
> because I don't know what DC to create a compatible bitmap to.

It's even worse. When no DC is available to create a compatible bitmap 
with, CreateBitmap has to be used, we knew this. But now I found this on 
the internet:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=OsQ0iiDP%24GA.236%40cppssbbsa04&rnum=3&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26q%3Dwin32%2Bcreatebitmap%2Bmemory%26btnG%3DGoogle%2BSearch

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Don't use CreateBitmap, use CreateDIBitmap or CreateCompatibleBitmap.
CreateDIBitmap & CreateCompatibleBitmap both will create a bitmap that 
is guaranteed to be compatible (ie can be blitted to) with the screen. 
In addition, CreateDIBitmap takes a pointer to a device independent 
bitmap (ie the data contained within a .bmp file).

CreateBitmap on the other hand will create the bitmap you specify, but 
if the cPlanes and cBitsPerPel settings do not match the current display
settings the bitmap can not be blitted to the display.
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So it's not even guaranteed to work :(. FYI: CreateDIBitmap, 
CreateCompatibleBitmap both need a DC.

Micha.