Thread: allegro flicker problem(mappy)

I am not familiar with the Allegro library, so you will need to refer to the documentation for specifics. However, there should probably be a way for you to tell the library to wait for a vertical retrace before pushing your back buffer to the display.

Basically your monitor is displaying a "new" image x times every second (x is your monitor's refresh rate, for example 85Hz is 85 times each second). Each time it displays a new image, the electron gun moves quickly from left to right for each line, and top line to bottom line for the screen. Then it has to travel back to the start position at the top left of the screen before it can display the next image. This is the vertical retrace, and is when you want to have the back buffer copied to the display buffer.

If you only push the back buffer to the display at this time (by having your program wait for a vsync signal, or whatever the Allegro library calls it) then you will not see any flicker. If you push the back buffer at any other time, then the electron gun is in the middle of drawing when the frame changes and causes the flicker you are seeing. (Flat panel displays don't use an electron gun, but it is the same principal.)

By having your program wait for that vsync signal (basically a signal from the monitor that it is retracing) before pushing the back buffer to the front, your double buffer will work exactly as you are expecting. The worst case scenario is that it will take so long for your program to process the next frame that the monitor will redraw the screen several times before you are ready to push the back buffer. This would still not flicker, it would instead show up as a lower framerate (choppy movement).

Unless the framerate drops down so low that you begin to notice the choppiness, you don't need to worry about improving the efficiency of how you read your map.

This applies whether you are using Allegro, DirectX or any other graphics library. In the end it is displayed on the monitor so you have to bow to the physics of the monitor.

Another guess is that perhaps you have the wrong variable somewhere. Check to make sure you are not calling one or more drawing functions with the wrong buffer variable. If you are, then you are probably drawing those elements to the screen buffer rather than the back buffer. If it was only pushing the back buffer to the screen buffer during the vsync, then there should not be any flickering.

Without seeing your code, we can only guess at what the problem might be.