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POOpenCL image2d and image3d memory layout
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copied!<p>When transferring a 2d image stored in host memory to OpenCL, how is it reading the values - row major or column major? Let's assume row major.</p> <pre><code>index = row*NUM_COLS + col </code></pre> <p>How about 3d image stored in host memory? I believe that's treated as a stack of 2D images (which was assumed to be row major). Then pixel (row,col,slice) for limits (NUM_ROWS,NUM_COLS,NUM_SLICES) in terms of OpenCL is at:</p> <pre><code>index = slice*NUM_ROWS*NUM_COLS + row*NUM_COLS + col </code></pre> <p>However, according to <a href="http://en.wikipedia.org/wiki/Row-major_order#Generalization_to_higher_dimensions" rel="nofollow">wikipedia</a> formulas the 3d Row Major indexing <strong>should</strong> be:</p> <pre><code>index = slice + NUM_SLICES*(col + NUM_COLS*row) = row*NUM_COLS*NUM_SLICES + col*NUM_SLICES + slices </code></pre> <p>According to same article Column Major Ordering access should be:</p> <pre><code>index = row + NUM_ROWS*(col + NUM_COLS*slice) = slice*NUM_ROWS*NUM_COLS + col*NUM_ROWS + row </code></pre> <p>None of which seems to match what OpenCL is doing in 3d case.</p> <p>So I guess I really have 2 questions</p> <ol> <li>How do I lay out my memory for transfering 2d and 3d images to OpenCL?</li> <li>Why does it seem like OpenCL has chosen a non standard memory layout in 3d case?</li> </ol> <p><strong>Edit</strong></p> <p>I view wikipedia article as a generic layout scheme. "row" or "column" are secondary label words. Whether you are dealing with tuples (row, col, slice) limited to (NUM_ROWS, NUM_COLS, NUM_SLICES) or (x,y,z) (WIDTH, HEIGHT, DEPTH) doesn't matter as long as it's consistent. It just tells you which dimension is continuous in memory. In "row major" it's the last dimension - z values that are next to each other, in column major it's the first dimension - x.</p> <p>So once again I think "row major" layout for x,y,z 3d image indexing should have been:</p> <pre><code>index = z + DEPTH * (y + HEIGHT * x) = x * HEIGHT * DEPTH + y * HEIGHT + z </code></pre> <p>It isn't. But, I suppose you can chose whatever scheme you want.</p>

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