How do you construct a scroller?

[Sushi]

I'm a newblet of a programmer, and need help understanding how a scroller is constructed. I'm trying to create something similar to UFO race in which you map a bitmap to a value in an array. I'm also trying to figure out how to move the the map in a variable direction, not just left right up and down. I don't really know the formulas. Can anybody explain it to me?

[ajsb113]

The way that I've done it is similar to the way Rodot did in UFO race. Have two ints cameraX and cameraY. If you're roaming on a map you can do this:

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cameraX = player.x - LCDWIDTH/2;
cameraY = player.y - LCDHEIGHT/2;


That should put the camera position to the top left of the screen and to draw:

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gb.display.drawBitmap(player.x - cameraX, player.y - cameraY, bitmap);


By subtracting camera value it will draw everything relative to the screen and the player, so the map will move with the player. I hope this helps