--- /dev/null
+#include <GL/glew.h>
+
+#include "fft_pass_effect.h"
+#include "effect_util.h"
+#include "util.h"
+
+FFTPassEffect::FFTPassEffect()
+ : input_width(1280),
+ input_height(720),
+ direction(HORIZONTAL)
+{
+ register_int("fft_size", &fft_size);
+ register_int("direction", (int *)&direction);
+ register_int("pass_number", &pass_number);
+ register_int("inverse", &inverse);
+ glGenTextures(1, &tex);
+}
+
+FFTPassEffect::~FFTPassEffect()
+{
+ glDeleteTextures(1, &tex);
+}
+
+std::string FFTPassEffect::output_fragment_shader()
+{
+ char buf[256];
+ sprintf(buf, "#define DIRECTION_VERTICAL %d\n", (direction == VERTICAL));
+ return buf + read_file("fft_pass_effect.frag");
+}
+
+void FFTPassEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
+{
+ Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+ int input_size = (direction == VERTICAL) ? input_height : input_width;
+
+ // See the comments on changes_output_size() in the .h file to see
+ // why this is legal. It is _needed_ because it counteracts the
+ // precision issues we get because we sample the input texture with
+ // normalized coordinates (especially when the repeat count along
+ // the axis is not a power of two); we very rapidly end up in narrowly
+ // missing a texel center, which causes precision loss to propagate
+ // throughout the FFT.
+ assert(*sampler_num == 1);
+ glActiveTexture(GL_TEXTURE0);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+ check_error();
+
+ // The memory layout follows figure 5.2 on page 25 of
+ // http://gpuwave.sesse.net/gpuwave.pdf -- it can be a bit confusing
+ // at first, but is classically explained more or less as follows:
+ //
+ // The classic Cooley-Tukey decimation-in-time FFT algorithm works
+ // by first splitting input data into odd and even elements
+ // (e.g. bit-wise xxxxx0 and xxxxx1 for a size-32 FFT), then FFTing
+ // them separately and combining them using twiddle factors.
+ // So the outer pass (done _last_) looks only at the last bit,
+ // and does one such merge pass of sub-size N/2 (FFT size N).
+ //
+ // FFT of the first part must then necessarily be split into xxxx00 and
+ // xxxx10, and similarly xxxx01 and xxxx11 for the other part. Since
+ // these two FFTs are handled identically, it means we split into xxxx0x
+ // and xxxx1x, so that the second-outer pass (done second-to-last)
+ // looks only at the second last bit, and so on. We do two such merge
+ // passes of sub-size N/4 (sub-FFT size N/2).
+ //
+ // Thus, the inner, Nth pass (done first) splits at the first bit,
+ // so 0 is paired with 16, 1 with 17 and so on, doing N/2 such merge
+ // passes of sub-size 1 (sub-FFT size 2). We say that the stride is 16.
+ // The second-inner, (N-1)th pass (done second) splits at the second
+ // bit, so the stride is 8, and so on.
+
+ assert((fft_size & (fft_size - 1)) == 0); // Must be power of two.
+ float *tmp = new float[fft_size * 4];
+ int subfft_size = 1 << pass_number;
+ double mulfac;
+ if (inverse) {
+ mulfac = 2.0 * M_PI;
+ } else {
+ mulfac = -2.0 * M_PI;
+ }
+
+ assert((fft_size & (fft_size - 1)) == 0); // Must be power of two.
+ assert(fft_size % subfft_size == 0);
+ int stride = fft_size / subfft_size;
+ for (int i = 0; i < fft_size; ++i) {
+ int k = i / stride; // Element number within this sub-FFT.
+ int offset = i % stride; // Sub-FFT number.
+ double twiddle_real, twiddle_imag;
+
+ if (k < subfft_size / 2) {
+ twiddle_real = cos(mulfac * (k / double(subfft_size)));
+ twiddle_imag = sin(mulfac * (k / double(subfft_size)));
+ } else {
+ // This is mathematically equivalent to the twiddle factor calculations
+ // in the other branch of the if, but not numerically; the range
+ // reductions on x87 are not all that precise, and this keeps us within
+ // [0,pi>.
+ k -= subfft_size / 2;
+ twiddle_real = -cos(mulfac * (k / double(subfft_size)));
+ twiddle_imag = -sin(mulfac * (k / double(subfft_size)));
+ }
+
+ // The support texture contains everything we need for the FFT:
+ // Obviously, the twiddle factor (in the Z and W components), but also
+ // which two samples to fetch. These are stored as normalized
+ // X coordinate offsets (Y coordinate for a vertical FFT); the reason
+ // for using offsets and not direct coordinates as in GPUwave
+ // is that we can have multiple FFTs along the same line,
+ // and want to reuse the support texture by repeating it.
+ int base = k * stride * 2 + offset;
+ int support_texture_index;
+ if (direction == FFTPassEffect::VERTICAL) {
+ // Compensate for OpenGL's bottom-left convention.
+ support_texture_index = fft_size - i - 1;
+ } else {
+ support_texture_index = i;
+ }
+ tmp[support_texture_index * 4 + 0] = (base - support_texture_index) / double(input_size);
+ tmp[support_texture_index * 4 + 1] = (base + stride - support_texture_index) / double(input_size);
+ tmp[support_texture_index * 4 + 2] = twiddle_real;
+ tmp[support_texture_index * 4 + 3] = twiddle_imag;
+ }
+
+ glActiveTexture(GL_TEXTURE0 + *sampler_num);
+ check_error();
+ glBindTexture(GL_TEXTURE_1D, tex);
+ check_error();
+ glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+ check_error();
+ glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+ check_error();
+ glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+ check_error();
+
+ // Supposedly FFTs are very sensitive to inaccuracies in the twiddle factors,
+ // at least according to a paper by Schatzman (see gpuwave.pdf reference [30]
+ // for the full reference), so we keep them at 32-bit. However, for
+ // small sizes, all components are exact anyway, so we can cheat there
+ // (although noting that the source coordinates become somewhat less
+ // accurate then, too).
+ glTexImage1D(GL_TEXTURE_1D, 0, (subfft_size <= 4) ? GL_RGBA16F : GL_RGBA32F, fft_size, 0, GL_RGBA, GL_FLOAT, tmp);
+ check_error();
+
+ delete[] tmp;
+
+ set_uniform_int(glsl_program_num, prefix, "support_tex", *sampler_num);
+ ++*sampler_num;
+
+ assert(input_size % fft_size == 0);
+ set_uniform_float(glsl_program_num, prefix, "num_repeats", input_size / fft_size);
+}
projects / movit / blobdiff