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  DrawArrays() GL_QUAD_STRIP, alpha value is ignored ???  (Read 2476 times)
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Offline blizzard

Senior Newbie





« Posted 2011-10-17 08:45:04 »

Hello

in the past I used the alpha value to set the transparence of a color:

gl2.glEnable(GL.GL_BLEND); // Turn Blending On
// set the color red, green, blue , alpha
gl2.glColor4f( color[1], color[2], color[3], color[0]  );

this worked well

Now I changed my code and use vbo´s and DrawArrays(..) and it look like the alpha value is ignored.
Do I have to set something special when I create the ColorPointer ?
Thanks

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   static void vboTestOnlyDrawSeveralQuadStrip(GL2 gl2){
     
      gl2.glEnable(GL.GL_BLEND); // Turn Blending On
     
      //--- turn shade Model Flat On
     // eaxh quad is filled with one color defined by the last vertex
     gl2.glShadeModel(GL2.GL_FLAT);
     
       for(int i=0; i<vboIndexArray.length/2; i++){
          // define which Types of Elements are a allowed
         gl2.glEnableClientState( GL2.GL_VERTEX_ARRAY );
          gl2.glEnableClientState( GL2.GL_COLOR_ARRAY );
       
          //--- set the vertex pointer
         // bind the buffer, from this moment this specific buffer is used
         gl2.glBindBuffer(GL2.GL_ARRAY_BUFFER, vboIndexArray[i]);
          // Get the Position of the data in the memory
         gl2.glVertexPointer(3, GL2.GL_FLOAT, 0, 0);
         
          //--- set the color pointer
            // bind the buffer, from this moment this specific buffer is used
         gl2.glBindBuffer(GL2.GL_ARRAY_BUFFER, vboIndexArray[i+(vboIndexArray.length/2)]);
          gl2.glColorPointer(4, GL2.GL_FLOAT, 0, 0);
                 
          // draw the Buffer
         gl2.glDrawArrays(GL2.GL_QUAD_STRIP, 0,((intCountOfQuads * 2) + 2));      
       
          // unbind the buffer, by using 0
         gl2.glBindBuffer(GL2.GL_ARRAY_BUFFER, 0);      
       
          // Disable vertex arrays
         gl2.glDisableClientState( GL2.GL_COLOR_ARRAY );
          gl2.glDisableClientState( GL2.GL_VERTEX_ARRAY );      
       }
     
   }//end: void vboTestOnlyDrawSeveralQuadStrip(






Offline princec

JGO Kernel


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« Reply #1 - Posted 2011-10-17 08:49:29 »

I don't see anywhere where you've specified what blending mode to use.

Cas Smiley

Offline blizzard

Senior Newbie





« Reply #2 - Posted 2011-10-17 09:08:38 »

Ah thank you that was a good hint ..

I forgot to copy 
gl2.glBlendFunc(GL.GL_SRC_ALPHA,GL.GL_ZERO);  // always drawn new

now it work :-)
thanks
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Offline theagentd
« Reply #3 - Posted 2011-10-17 09:10:19 »

That would discard the color already there? Isn't glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) the standard blending function for basic 2D blending? GL_ZERO would discard what is already there... >_<

Myomyomyo.
Offline R.D.

Senior Member


Medals: 2
Projects: 1


"For the last time, Hats ARE Awesome"


« Reply #4 - Posted 2011-10-26 12:19:00 »

Maybe he wants something like the DEPTH_TEST? So pixels with a smalle depth will simply be ignored? (Guess this good be used nicely in a map where you render the closest layer first and so on)
Offline theagentd
« Reply #5 - Posted 2011-10-27 09:12:48 »

He seems to just want to do finalColor = color * alpha, so I think his problem is resolved already.

Myomyomyo.
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