Use your 3D card's alpha blitting hardware. I'm doing this and have no problems doing 75 FPS on a PII 400 w/RIVA TNT and about 1/2 the screen full of alpha blits.
I believe there's an article by Tobias that explains the process; search for "Enhanced2D."
Mason McCuskey
Spin Studios
www.spin-studios.com
The other suggestion I have (if you're not already using it) is to draw your map to a memory buffer instead of directly to the back buffer. This removes the need for your alpha function to look up video memory, which will save time. Once you've applied your alpha (or lookup table, this should speed up either) to the memory buffer, use BltFast to draw it to the back buffer for best results (this way system -> video hardware acceleration will be used also, if available). If you're drawing your map with a lot of overlap, this might even speed up your initial framerate. Then again, it may also drop it if you aren't drawing a lot of overlap, but in the case of the alpha blending it's worth a try to see if it helps things. It does depend on other factors of your program and hardware, so play around with it and see what you come up with.
Good luck, and post back to the thread if you need any further help.
Starfall
[This message has been edited by Starfall (edited November 02, 1999).]
starfall: how would I make a function that shifts down the red and green pixels fast? I editied my alpha blitting function to make is so it does what you said, but it still goes pretty slow. What it does is go through a two loops (one for x, one for y) and changes each pixel on the back buffer (which is in video memory) to only the blue value of that pixel. It does this by ANDing the pixel with a blue mask. This isn't exactly what I want, but I'm not going to fix it if it won't go any faster. What should I do to make it faster?
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- mallen22@concentric.net
- http://members.tripod.com/mxf_entertainment/
[This message has been edited by Matthew Allen (edited November 02, 1999).]
If the surface you are locking and reading from is in VRAM, your frame rate is going to drop significantly. Unless all your sprites fit into VRAM, and since you are doing alpha blends, you need to do your image blting first to a system surface, do your blending there, then blast the whole image (or the dirty rect of it) up to the video surface, then call flip. Reads from VRAM are REALLY REALLY slow..
Actually Starfall, market research shows that the majority of gamers (in the US, anyway) have a card with some form of 3D acceleration. DirectX takes care of the differences between 3D cards, so if you write the code correctly, it will work on many more systems than just your own.
Mason McCuskey
Spin Studios
www.spin-studios.com
or I could be just rambling.
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- mallen22@concentric.net
- http://members.tripod.com/mxf_entertainment/
In reply to Mason, if "many more systems than just your own" is good enough for you, so be it. Personally I'd want my software to run on as many systems as possible, and without providing a software alternative you're cutting off a large portion of prospective users. The answer is of course simple, if you want the best of both worlds - offer both.
Regards
Starfall
