Drawing multiple Textures as tilemap
- by DocJones
I am trying to draw a 2d game map and the objects on the map in a single pass.
Here is my OpenGL initialization code
// Turn off unnecessary operations
glDisable(GL_DEPTH_TEST);
glDisable(GL_LIGHTING);
glDisable(GL_CULL_FACE);
glDisable(GL_STENCIL_TEST);
glDisable(GL_DITHER);
glEnable(GL_BLEND);
glEnable(GL_TEXTURE_2D);
// activate pointer to vertex & texture array
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
My drawing code is being called by a NSTimer every 1/60 s.
Here is the drawing code of my world object:
- (void) draw:(NSRect)rect withTimedDelta:(double)d {
GLint *t;
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, [_textureManager textureByName:@"blocks"]);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
for (int x=0; x<[_map getWidth] ; x++) {
for (int y=0; y<[_map getHeight] ; y++) {
GLint v[] = {
16*x ,16*y,
16*x+16,16*y,
16*x+16,16*y+16,
16*x ,16*y+16
};
t=[_textureManager getBlockWithNumber:[_map getBlockAtX:x andY:y]];
glVertexPointer(2, GL_INT, 0, v);
glTexCoordPointer(2, GL_INT, 0, t);
glDrawArrays(GL_QUADS, 0, 4);
}
}
}
(_textureManager is a Singelton only loading a texture once!)
The object drawing codes is identical (except the nested loops) in terms of OpenGL calls:
- (void) drawWithTimedDelta:(double)d {
GLint *t;
GLint v[] = {
16*xpos ,16*ypos,
16*xpos+16,16*ypos,
16*xpos+16,16*ypos+16,
16*xpos ,16*ypos+16
};
glBindTexture(GL_TEXTURE_2D, [_textureManager textureByName:_textureName]);
t=[_textureManager getBlockWithNumber:12];
glVertexPointer(2, GL_INT, 0, v);
glTexCoordPointer(2, GL_INT, 0, t);
glDrawArrays(GL_QUADS, 0, 4);
}
As soon as my central drawing routine calls the two drawing methods the second call overlays the first one. i would expect the call to world.draw to draw the map and "stamp" the objects upon it. Debugging shows me, that the first call is performed correctly (world is being drawn), but the following call to all objects ONLY draws the objects, the rest of the scene is getting black.
I think i need to blend the drawn textures, but i cant seem to figure out how.
Any help is appreciated.
Thanks
PS: Here is the github link to the project. It may not be in sync of my post here, but for some more in-depth analysis it may help.
