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SDL - Camera Movement


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#1 MrTheFoxx   Members   -  Reputation: 100

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Posted 25 November 2011 - 05:59 PM

My progress was going well until I realized that I'm going to need some sort of camera movement in my levels. At first, I felt that I could just have each tile moved as the player moves and that would be camera movement from one part of the level to the next. Is there a more efficient way to do this, such as having the viewing area itself follow the player instead of leaving it in one place and moving each and every part of the area (including enemies and other things) based on player movement? Thank you! ^^

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#2 MichaelStahre   Members   -  Reputation: 100

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Posted 13 December 2011 - 07:55 AM

This isn't really an SDL-specific solution, but when drawing with any library you'll always be specifying where on the screen you want to draw.

As I only have square-drawing SDL code lying around, I'll throw you an example where the player is drawn on the screen in the form of a small, black square.

Here, position is a struct containing the x-position and the y-position of the player.

    SDL_Rect player_rect = {position.x, position.y, 30, 30};
    SDL_FillRect(screen, &player_rect, SDL_MapRGB(screen->format, 0x00, 0x00, 0x00));


If you then want a camera, then one simple solution is to have a camera struct that's just like the position struct and use that as an offset.
    SDL_Rect player_rect = {position.x - camera.x, position.y - camera.y, 30, 30};
    SDL_FillRect(screen, &player_rect, SDL_MapRGB(screen->format, 0x00, 0x00, 0x00));


If you always subtract the position you want to draw to with the position of the camera whenever you draw something, including the stage geometry, then you can just move the camera and everything else will be properly offset.
If moving the player then also moves the camera then the player is free to move throughout the stage and will always be drawn at the same position relative to the camera while the rest of the stage will stay put.


There are better and/or more sophisticated solutions, but that should probably serve your most basic needs.
I don't know if SDL has any built-in camera functionality, but I know there are frameworks that do (such as XNA, where SpriteBatch can take the camera offset as a parameter.)

#3 MrTheFoxx   Members   -  Reputation: 100

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Posted 18 December 2011 - 02:18 PM

Thanks for the input. However, this was what I was describing, the theorem you mentioned. The problem with it is that the upper-left-hand-corner of the screen itself stays locked at 0, 0. Anything that attempts to pass that boundary can't and is therefore locked at 0, 0 as well. So let's say the player was going screen right. Everything was moving screen left as to keep the whole thing in the viewing range and to show that the stage was moving. Whenever the stage parts collided with the left-most side of the screen, they didn't go beyond that and began cumulating at that part of the screen. Then, when the player decided to move screen left, they couldn't due to this same problem, and the stage wouldn't properly move to the right to show camera movement. All of the parts that met 0, 0 retained that value and were moving at the same rate. This is kind of difficult to explain. I will provide a set of diagrams if necessary.

Instead, it would be better if the viewing range (0,0 to 640, 480) moved with the player and we saw different regions of the screen without having to go about subtracting or adding to the enemies, map tiles, and so on. How to do that was my initial question. It doesn't seem impossible.




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