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POError with GL_TRIANGLE_STRIP and vertex array
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  1. POError with GL_TRIANGLE_STRIP and vertex array
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    copied!<p>I have this method that prepares the coordinates in the posCoords array. It works properly about 30% of the time, then the other 70% the first few triangles are messed up in the grid. The entire grid is drawn using GL_TRIANGLE_STRIP. I'm pulling my hair out trying to figure out whats wrong. Any ideas?</p> <p><img src="https://i.stack.imgur.com/SVZDX.jpg" alt="enter image description here"></p> <p><img src="https://i.stack.imgur.com/DtdeF.jpg" alt="enter image description here"></p> <pre><code>if(!ES2) { glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); } int cols = floor(SCREEN_WIDTH/blockSize); int rows = floor(SCREEN_HEIGHT/blockSize); int cells = cols*rows; NSLog(@"Cells: %i", cells); coordCount = /*Points per coordinate*/2 * /*Coordinates per cell*/ 2 * cells + /* additional coord per row */2*2*rows; NSLog(@"Coord count: %i", coordCount); if(texCoords) free(texCoords); if(posCoords) free(posCoords); if(dposCoords) free(dposCoords); texCoords = malloc(sizeof(GLfloat)*coordCount); posCoords = malloc(sizeof(GLfloat)*coordCount); dposCoords = malloc(sizeof(GLfloat)*coordCount); int index = 0; float lowY, hiY = 0; int x,y = 0; BOOL drawLeftToRight = YES; for(y=0;y&lt;SCREEN_HEIGHT;y+=blockSize) { lowY = y; hiY = y + blockSize; // Draw a single row for(x=0;x&lt;=SCREEN_WIDTH;x+=blockSize) { CGFloat px,py,px2,py2 = 0; // Top point of triangle if(drawLeftToRight) { px = x; py = lowY; // Bottom point of triangle px2 = x; py2 = hiY; } else { px = SCREEN_WIDTH-x; py = lowY; // Bottom point of triangle px2 = SCREEN_WIDTH-x; py2 = hiY; } // Top point of triangle posCoords[index] = px; posCoords[index+1] = py; // Bottom point of triangle posCoords[index+2] = px2; posCoords[index+3] = py2; texCoords[index] = px/SCREEN_WIDTH; texCoords[index+1] = py/SCREEN_HEIGHT; texCoords[index+2] = px2/SCREEN_WIDTH; texCoords[index+3] = py2/SCREEN_HEIGHT; index+=4; } drawLeftToRight = !drawLeftToRight; } </code></pre>
 

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