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  How do I load from a sprite atlas?  (Read 754 times)
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Offline dah01

Junior Member


Medals: 7



« Posted 2011-12-19 03:38:25 »

This was answered in another thread. I accidentally double submitted.
http://www.java-gaming.org/topics/using-lwjgl-and-slick2d-how-do-i-load-and-display-sprites-from-a-sprite-atlas/25325/view/topicseen.html
Offline Thau

Junior Newbie





« Reply #1 - Posted 2011-12-19 14:50:44 »

I did it by using glTexCoord2f. This way I'm only drawing part of the sprite sheet, instead of the entire thing. This might not be the way to do it (I'm still learning) but it works. Example of my draw method below (again, I'm still learning OpenGL, and I suck at the simplest of maths. so if there's anything retarded in there, please point it out  Wink )

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public void draw(float posX, float posY) {
      GL11.glPushMatrix();
     
      GL11.glEnable(GL11.GL_TEXTURE_2D);
      GL11.glTexEnvf(GL11.GL_TEXTURE_ENV, GL11.GL_TEXTURE_ENV_MODE, GL11.GL_REPLACE);

      texture.bind();
     
      GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MIN_FILTER, GL11.GL_NEAREST);
      GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MAG_FILTER, GL11.GL_NEAREST);
      GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_T, GL12.GL_CLAMP_TO_EDGE);
     
      float spriteWidth = (float) ((getWidth() / (float) columns) / getWidth());
      float spriteHeight = (float) (getHeight() / rows) / getHeight();
     
       
      float textureX1;
      float textureX2;
     
      if (orientation == MIRRORED) {
         textureX1 = (float) -(columns * spriteWidth) + (spriteWidth * ((currentTextureIndex % columns)+1));
         textureX2 = textureX1 - spriteWidth;
      } else {
         textureX1 = (float) (spriteWidth) * (currentTextureIndex % columns);
         textureX2 = textureX1 + spriteWidth;
      }
     
      float textureY1 = (float) (spriteHeight) * (currentTextureIndex / rows) % rows;
      float textureY2 = textureY1 + spriteHeight;
     

      GL11.glBegin(GL11.GL_QUADS);
      GL11.glTexCoord2f(textureX1, textureY1);
      GL11.glVertex2f(posX, posY);
      GL11.glTexCoord2f(textureX2, textureY1);
      GL11.glVertex2f(posX + spriteSize, posY);
      GL11.glTexCoord2f(textureX2, textureY2);
      GL11.glVertex2f(posX + spriteSize, posY + spriteSize);
      GL11.glTexCoord2f(textureX1, textureY2);
      GL11.glVertex2f(posX, posY + spriteSize);
      GL11.glEnd();

      GL11.glPopMatrix();
   }


EDIT: might be worth mentioning that this only works with sprite sheets/atlases where all the sprites are the same size
EDIT2: perhaps I should finish reading your entire code next time, it seems you are doing something similar in your code? but you're drawing the entire sheet in one loop? you're not treating each tile as a separate entity then? now I've gone got myself all confused... perhaps I'm in over my head Tongue
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