void
render_quad(float x, float y, float width, float height) {
GLfloat vertices[] = {x + width, y + height,
x, y + height,
x, y,
x + width, y };
GLfloat texCoords[] = {1.0, 1.0,
0.0, 1.0,
0.0, 0.0,
1.0, 0.0 };
GLubyte indices[] = {0, 1, 2, 0, 2, 3};
//Set color variable before rendering quad
set_uniform_vec4(colorUni, colorRed, colorGreen, colorBlue, colorAlpha);
set_uniform_float(diffuseSamplerUni, 0);
if (currentTexture != NULL) bind_texture(currentTexture, 0);
else bind_texture(whiteTexture, 0);
glEnableVertexAttribArray(vertPosAttrib->handle);
glEnableVertexAttribArray(texCoordAttrib->handle);
glVertexAttribPointer(vertPosAttrib->handle, 2, GL_FLOAT, GL_FALSE, 0, vertices);
glVertexAttribPointer(texCoordAttrib->handle, 2, GL_FLOAT, GL_FALSE, 0, texCoords);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_BYTE, indices);
glDisableVertexAttribArray(vertPosAttrib->handle);
glDisableVertexAttribArray(texCoordAttrib->handle);
unbind_texture(0);
}
void FFTPassEffect::set_gl_state(GLuint glsl_program_num, const 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);
}
