AlphaBlit
void AlphaBlit(int x, int y, int source_image, int alpha_image, int dest_image)
Documentation
Before I go into this function let me explain what a mask is.
A mask is a grayscale (essentially, black and white) image that is applied to another image to tell the computer how much transparency is allowed in different places. By using a mask you can blit anti-aliased images and other things for a higher image quality. If used properly you can eliminate the hard edges you might often get with TBlit.
AlphaBlit blits image source_image to image dest_image at cooridinates (x, y), with the alphamask alpha_image.
Note: source_image and alpha_image must have be the exact same dimensions in pixels.
Example Usage
int portrait = LoadImage("Hero.png");
int portrait_mask = LoadImage("Hero_mask.png");
AlphaBlit(0, 0, portrait, portrait_mask, screen);Talkback #2 written by Technetium on 2012-01-05.
Note that this function completely ignores setLucent() values. If you want to have an image with both an alpha mask and a general translucency value (such as if you want an anti-aliased image that fades in or fades out), the best way to do this is to edit the mask image. So you have a source_image and alpha_image, and then you need a 3rd image so you don't have to keep reloading a fresh alpha_image to edit. So let's make the 3rd image called alpha_original. Obviously all three images need to be the same dimensions.
For any time when you want to AlphaBlit the image at a certain translucency, use the following method. First, set up the images:
int source_image = loadimage("my_image.pcx");
int alpha_original = loadimage("my_image_alpha.pcx");
int alpha_image = newImage(imagewidth(source_image),imageHeight(source_image));
Then when you actually want to display the image with both alpha and transparency:
Blit(0,0,alpha_original,alpha_image); setlucent(50); //or whatever rectfill(0,0,imagewidth(source_image),image_height(source_image),RGB(0,0,0),alpha_image); setlucent(0); AlphaBlit(x,y,source_image,alpha_image,screen);
The rectfill will darken each pixel of the mask appropriately. It should work exactly as it would if AlphaBlit used setlucent values.
Editing the alpha masks is an extremely powerful technique for creating effects on images without altering the original.
Talkback #1 written by verge-rpg.com on 2012-01-05.
This is the talkback thread for the documentation page: alphablit
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