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OpenGL Efficient iso-map rendering

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Hey guys,

I'm having some trouble by rendering an isometric, tile-based map. Lets say I've a staggered tile map like http://www.noblemast...ghtmap-Java.jpg or http://images.gamede...ap_TestMap1.gif which is 1024 tiles width and height.

I just reduced the number of tiles which should be drawn because not all 1024x1024 tiles are displayed at once. To more improve the rate of fps, I render the complete map in one big display list. But this seems to be a little problem. I'm currently using the following code to render my map:

glNewList(displayList, GL_COMPILE);

glPushMatrix();

glTranslatef(-offset.x, -offset.y, 0);

for (int y = fromY; y < toY && y < tiles.length; y++) {

for (int x = fromX; x < toX && x < tiles[y].length; x++) {
tiles[y][x].draw();
}
}
glPopMatrix();

glEndList();


Where fromX/Y and toX/Y defines the range of tiles which should be drawn. tiles[y][x].draw() calls the following:

glBindTexture(GL_TEXTURE_2D, texId);

glBegin(GL_QUADS);

glTexCoord2f(0, 0);
glVertex3f(x, y, z);

glTexCoord2f(1, 0);
glVertex3f(x + w, y, z);

glTexCoord2f(1, 1);
glVertex3f(x + w, y + h, z);

glTexCoord2f(0, 1);
glVertex3f(x, y + h, z);

glEnd();


A third method simply calls glCallList(displayList) and updates these displaylist if needed.

When I run my game, it first starts with around 1500 fps (all tiles having the same texture)... but when I increment my tiles to create a height-map, the fps rate is dropping down to around 300 or 500 fps (only for the map, nothing else). Okay... I already know that I should prevent senseless/redundant calls of glBegin()/glEnd() and glBindTexture, so the first thing which should be improved is the draw()-method. My first idea was to add the tiles which should be drawn to an associative array and sort them by the internal texture id of OpenGL. This works with a little problem - I always have to clear and rehash this array which takes some time and it drops my game down to 1 fps after some seconds. The next idea is that I can use texture atlases - this would prevent each glBind() and glBegin()/glEnd() in the draw()-method but what about other graphics, let's say buildings or similar graphics which have nothing to do with the surface? So I'm thinking of using techniques likes VBA's or VBO's... but I currently having no idea how I can use these to draw my map as efficient as possible.


I hope anyone can help to improve my map :)

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