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Iso Optimization

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Hi, i recently started changing over my square tile-based game into an isometric tile game and am running into a few difficulties. I finally got the rendering/mouse mapping working, but am having trouble optimizing the rendering so that i''m not blitting too much offscreen. I went out and bought Pazera''s Iso book, but don''t understand some little things. Just to get the rendering working I was blitting every tile in my 50x60 tile map. (about 3000 blits per frame!) I noticed how slow this was already even on my 500mhz system. There''s a section in the book on how to optimize this, but for diamond shaped maps I don''t understand how I am supposed to blit from west to east (left to right) when all my tiles'' x coordinates increase diagonally? Just as a test I put something like: // if tile is on the screen then blit it if((tile.x > -64)&&(tile.x < SCREEN_WIDTH)&& (tile.y > -32)&&(tile.y < SCREEN_HEIGHT)) blit tile This works alot better (blitting about 280 tiles/frame), but still seems like the loop itself is inefficient. If anyone can explain Pazerra''s optimization for diamond maps, that would be great, or even if you know other ways i can optimize the rendering. Thanks Alot BC - Free Your Mind -

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void CMapView::Draw()
SDL_Rect rect;
SDL_Surface *tile;

int x, y;

// Get the coordinates of the upper left tile
GetCellCoordinates((int)(MapX), (int)(MapY), &x, &y);

int screen_x = (x << 5) - (y << 5) - 32 - (int)(MapX);
int screen_y = (y << 4) + (x << 4) - (int)(MapY);

// To avoid jagged edges start drawing one tile up and to the left
screen_x -= 32;
screen_y -= 16;

int orig_x = x;
int orig_y = y;

int orig_screen_x = screen_x;

int row = 0;

SDL_FillRect(Buffer, NULL, 0);

while(screen_y < ScreenHeight)
while(screen_x < ScreenWidth)
if((x >= 0) && (y >= 0) && (x < Map.GetWidth()) && (y < Map.GetHeight()))
rect.x = screen_x;
rect.y = screen_y;
tile = Map(x, y)->Tile.GetCurrentFrame();
SDL_BlitSurface(tile, NULL, Buffer, &rect);
Map(x, y)->Tile.Update();
screen_x += 64;
screen_x = orig_screen_x + ((row & 1) << 5);
screen_y += 16;
orig_x += row & 1;
x = orig_x;
orig_y += 1 - (row & 1);
y = orig_y;
rect.x = X;
rect.y = Y;
SDL_BlitSurface(Buffer, NULL, Screen, &rect);

Ok this is the code I use. Essentialy I find out what tile is in the top left corner. Then I start drawing from left to right top to bottom on the screen. Note that when I do this I must move diagonally on the actual map. This way I never even check tiles that ar not on the screen.

This code is for diamond shaped maps, and works with smooth scrolling.

It may be hard to read because I have at least tried to optimize it any way I could. "x << 5" for example means is the same as "x * 32" and "x & 1" is the same as "x % 2" except they are much faster(and only works with numbers that are powers of 2).

[edited by - robinei on July 19, 2002 11:08:01 PM]

[edited by - robinei on July 19, 2002 11:18:14 PM]

[edited by - robinei on July 19, 2002 11:19:00 PM]

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I''m currently coding an isometric engine myself. Regarding this optimization thing, what I do is create a dirty tiles list. Dirty tiles means those that are visible and needs to be redrawn. Though my map is a two-dimensional array, the dirty tiles list is a simple linear list. As far as i can tell, this is a big help in the efficiency of my drawing code.

As for generating the list itself, it only needs to be done when the display state changes -- i.e., scrolling and panning, creatures moved/changed state, etc.

I''m trying to think of a way to make this faster still by simple pruning and adding to the dirty tiles list instead of generating the whole thing everytime it''s needed.

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