void blur(std::string suffix, ImageParam input) { input.set_bounds(2, 0, CHANNELS).set_stride(0, CHANNELS).set_stride(2, 1); Var x("x"), y("y"), c("c"); Func clamped("clamped"); clamped = BoundaryConditions::repeat_edge(input); Func blur_x("blur_x"); blur_x(x, y, c) = (clamped(x - 1, y, c) + clamped(x, y, c) + clamped(x + 1, y, c)) / 3; Func result("result"); result(x, y, c) = (blur_x(x, y - 1, c) + blur_x(x, y, c) + blur_x(x, y + 1, c)) / 3; result.output_buffer().set_bounds(2, 0, CHANNELS).set_stride(0, CHANNELS).set_stride(2, 1); Target target = get_target_from_environment(); result.bound(c, 0, CHANNELS) .reorder_storage(c, x, y) .reorder(c, x, y); if (target.has_gpu_feature() || target.has_feature(Target::OpenGLCompute)) { result.vectorize(c, 4) .gpu_tile(x, y, 64, 64); } else { Var yi("yi"); result .unroll(c) .split(y, y, yi, 32) .parallel(y) .vectorize(x, 4); blur_x.store_at(result, y) .compute_at(result, yi) .reorder(c, x, y) .unroll(c) .vectorize(x, 4); } std::string filename("avg_filter"); result.compile_to_file(filename + suffix, {input}); }
Func build() { // Define the Func. Func brighter("brighter"); brighter(x, y, c) = input(x, y, c) + offset; // Schedule it. brighter.vectorize(x, 16); // We will compile this pipeline to handle memory layouts in // several different ways, depending on the 'layout' generator // param. if (layout == Layout::Planar) { // This pipeline as written will only work with images in // which each scanline is densely-packed single color // channel. In terms of the strides described in lesson // 10, Halide assumes and asserts that the stride in x is // one. // This constraint permits planar images, where the red, // green, and blue channels are laid out in memory like // this: // RRRRRRRR // RRRRRRRR // RRRRRRRR // RRRRRRRR // GGGGGGGG // GGGGGGGG // GGGGGGGG // GGGGGGGG // BBBBBBBB // BBBBBBBB // BBBBBBBB // BBBBBBBB // It also works with the less-commonly used line-by-line // layout, in which scanlines of red, green, and blue // alternate. // RRRRRRRR // GGGGGGGG // BBBBBBBB // RRRRRRRR // GGGGGGGG // BBBBBBBB // RRRRRRRR // GGGGGGGG // BBBBBBBB // RRRRRRRR // GGGGGGGG // BBBBBBBB } else if (layout == Layout::Interleaved) { // Another common format is 'interleaved', in which the // red, green, and blue values for each pixel occur next // to each other in memory: // RGBRGBRGBRGBRGBRGBRGBRGB // RGBRGBRGBRGBRGBRGBRGBRGB // RGBRGBRGBRGBRGBRGBRGBRGB // RGBRGBRGBRGBRGBRGBRGBRGB // In this case the stride in x is three, the stride in y // is three times the width of the image, and the stride // in c is one. We can tell Halide to assume (and assert) // that this is the case for the input and output like so: input .set_stride(0, 3) // stride in dimension 0 (x) is three .set_stride(2, 1); // stride in dimension 2 (c) is one brighter.output_buffer() .set_stride(0, 3) .set_stride(2, 1); // For interleaved layout, you may want to use a different // schedule. We'll tell Halide to additionally assume and // assert that there are three color channels, then // exploit this fact to make the loop over 'c' innermost // and unrolled. input.set_bounds(2, 0, 3); // Dimension 2 (c) starts at 0 and has extent 3. brighter.output_buffer().set_bounds(2, 0, 3); // Move the loop over color channels innermost and unroll // it. brighter.reorder(c, x, y).unroll(c); // Note that if we were dealing with an image with an // alpha channel (RGBA), then the stride in x and the // bounds of the channels dimension would both be four // instead of three. } else if (layout == Layout::Either) { // We can also remove all constraints and compile a // pipeline that will work with any memory layout. It will // probably be slow, because all vector loads become // gathers, and all vector stores become scatters. input.set_stride(0, Expr()); // Use a default-constructed // undefined Expr to mean // there is no constraint. brighter.output_buffer().set_stride(0, Expr()); } else if (layout == Layout::Specialized) { // We can accept any memory layout with good performance // by telling Halide to inspect the memory layout at // runtime, and branch to different code depending on the // strides it find. First we relax the default constraint // that stride(0) == 1: input.set_stride(0, Expr()); // Use an undefined Expr to // mean there is no // constraint. brighter.output_buffer().set_stride(0, Expr()); // The we construct boolean Exprs that detect at runtime // whether we're planar or interleaved. The conditions // should check for all the facts we want to exploit in // each case. Expr input_is_planar = (input.stride(0) == 1); Expr input_is_interleaved = (input.stride(0) == 3 && input.stride(2) == 1 && input.extent(2) == 3); Expr output_is_planar = (brighter.output_buffer().stride(0) == 1); Expr output_is_interleaved = (brighter.output_buffer().stride(0) == 3 && brighter.output_buffer().stride(2) == 1 && brighter.output_buffer().extent(2) == 3); // We can then use Func::specialize to write a schedule // that switches at runtime to specialized code based on a // boolean Expr. That code will exploit the fact that the // Expr is known to be true. brighter.specialize(input_is_planar && output_is_planar); // We've already vectorized and parallelized brighter, and // our two specializations will inherit those scheduling // directives. We can also add additional scheduling // directives that apply to a single specialization // only. We'll tell Halide to make a specialized version // of the code for interleaved layouts, and to reorder and // unroll that specialized code. brighter.specialize(input_is_interleaved && output_is_interleaved) .reorder(c, x, y).unroll(c); // We could also add specializations for if the input is // interleaved and the output is planar, and vice versa, // but two specializations is enough to demonstrate the // feature. A later tutorial will explore more creative // uses of Func::specialize. // Adding specializations can improve performance // substantially for the cases they apply to, but it also // increases the amount of code to compile and ship. If // binary sizes are a concern and the input and output // memory layouts are known, you probably want to use // set_stride and set_extent instead. } return brighter; }