spot light effect in platform game

what would be a good way to simulate a spot light effect for a 2d game ?

the way i would do it if i could - would be to draw everything on the backbuffer, put a mask on it in the shape of a triangle (well something more complex but triangle would do for now) and then flip to the primary ...

the thing is i want to be able to rotate the mask so that i could have my hero holding a torch so when he walks around all you see is a tirangle infront of him and nothing else ...

more advanced i would want to have tranperancy on the edges of the triangle but not required at this moment....

any advice would be great .. thanks
note - i am using dx7

For rotation: Simple 90 degree rotation is easy. Get the new Pixel X and Y with this:

VB Code:

NewX = Width - Y
NewY = X

So, you can manually SetPixel/GetPixel your way out of that one. Actually, just saw you were doing directdraw.. so get/setlockedpixel or getlockedarray would be what you're looking for.

well the rotation angle is incremented by about 5 degress everytime you press left or right .. so not just 90 degree rotations.

well what i am really asking i guess is the funtion that creats the mask. i never had to do masking before but what i have read is that it is used to create transparency effect.

from what i understant you need to have a bitmap in the shape of the mask you want. the thing is; the light effect will be pretty big. over all about 30 percent of the screen... so the concern becomes would masking with such a big bitmap slow down the computer (if it works the way i think it does) .... also i would need to rotate the bitmap by some angle each time and then apply it as a mask.

so it seems this would create alot of load and slow down the game ...

is this how it is done ?

note: when i mean mask i guess i am refering to the effect achived using photoshop mask ... putting a layer over a picture with a hole in it ...

Yeah, it would create tons of overhead. Listen, if you're looking to create a game with that much scale, just go full out 3D. You can't get this kind of speed in VB.... But anyway. I suggest doing the game at a smaller scale, or limiting the size of the flashlight (just a small cone, maybe one that fades out).