This is a more updated version of the previous example. The only real difference is that, this one uses built maps where is the original one demonstrates the hands on method. Apart from that they're pretty much the same, with just some tweaks for newer editions of PlayBasic V1.64M and above.
This is another short PlayBasic source code example, this one's demonstrating a selective redrawing method using PlayBasic Maps. The program attempts to reduce the cost per refresh by not redrawing the entire backdrop picture every frame. It does this by tagging the overdrawn zones that need to be restored using a Map. So basically the backdrop picture is first cut up into an Map representation. In this example the block size is 32x by 32y pixels, giving us a level size of (800/32 by 600/32). The demo uses two versions of the level tile map data. One is the original and the second is a version we're going to draw from. We need two since the redraw version gets cleared and altered each frame.
When drawing character objects (in this demo those are the circular blobs), we move the object then convert it's 2d space coordinates back into map coordinates. Then copy from this tile/block area from Original Level to the Refresh Level. We repeat this process for all on screen objects. So after processing our characters, the refresh map contains the parts of the backdrop that need to refreshed (reset) back to it's original state before drawing the next frame. So rather than redraw the entire backdrop picture every time, we can selectively refresh the backdrop. This type of method works really well in 2D games, as it allows the program to lower the cost per-pixel, ironing out the performance for older systems. By older, I mean systems beyond 5 years, closer to 10 years old really
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