[fpc-pascal] Implementing AggPas with PtcGraph

[James Richters]

I've figured out a way to get my animations to work fast and still have the quality of aggpas.  The problem I have is that even though I've managed to accelerate putimage() and it's pretty fast, it's still not fast enough and my animations in my program happen too slow, especially on slow computers.  I can build the screen fast with aggpas, and I can do putimage() pretty fast, but for some reason making a change with aggpas then putimage, then change aggpas then putimage... is slower.  So I came up with a solution.  I do the animations with ptcgraph commands at the same time I build the screen with aggpas, then when the animation is finished, I do my putimage() and replace the screen with the aggpas rendered version.  It works out that during the animation, the screen is changing distractingly fast that you really don't notice the lower quality graphics produced by ptcgraph routines, and when it stops and now you have a chance to look a it, the screen has been replaced with the aggpas version so everything looks nice and smooth 😊   With this method I actually had to put a delay in my animation cycle or it was too fast and I lost the animation effect I was looking for.   

Now I'm ready to start integrating everything I learned into my real application and I have a question.
My original application used only 8bit colors, but now I am upgrading it to 16bit colors because it will give aggpas more to work with for it's anti-aliasing.   Is there some formula or maybe even some function in freepascal somewhere that converts 8bit colors to their 16bit equivalents?   The two color schemes are nothing alike.  16bit is using this RGB565 format, but 8bit colors (at least the version I was using) the colors have no real relation to their bits (see this https://pasteboard.co/2K38l6Gk1.png)  I can't figure out any pattern to this at all and while some colors I can figure out, others would be quite difficult.  I'm wondering if maybe there is already some translation from these 8bit color designations into 16bit color designations so all I would have to do is a global search and replace of setcolor(x) to setcolor(8bit_to_16bit(x)); and then all my colors would be the same as they were.

I'm also wondering if there is already some function to either convert the 16bit RGB565 colors into separate 8bit values of red, green, and blue suitable to plug into aggpas procedures like 
agg^.lineColor(red, green, blue, 255);  I could probably manage something for this because it's pretty well defined that I have 5bits red, 6 bits green, and 5 bits blue, but still I'm not exactly clear how it would get from 5 or 6 bits up to 8 bits per color...  but if it's already available somewhere I might as well use what's done already.

James