X-Git-Url: https://git.sesse.net/?p=movit;a=blobdiff_plain;f=resample_effect.cpp;h=9c8caf3bb77ed58bf2d143dcc2b3b837b81a001c;hp=244a3e2a6081187f19962b531c7fa86dde46203b;hb=2fd06b9c44225d1e740cb2de08a9dfa5c9cd0031;hpb=6c954b4f0bff0743e13ce6ddcee8bda15b3af234 diff --git a/resample_effect.cpp b/resample_effect.cpp index 244a3e2..9c8caf3 100644 --- a/resample_effect.cpp +++ b/resample_effect.cpp @@ -1,4 +1,6 @@ // Three-lobed Lanczos, the most common choice. +// Note that if you change this, the accuracy for LANCZOS_TABLE_SIZE +// needs to be recomputed. #define LANCZOS_RADIUS 3.0 #include @@ -40,15 +42,67 @@ float sinc(float x) } } -float lanczos_weight(float x, float a) +float lanczos_weight(float x) { - if (fabs(x) > a) { + if (fabs(x) > LANCZOS_RADIUS) { return 0.0f; } else { - return sinc(M_PI * x) * sinc(M_PI * x / a); + return sinc(M_PI * x) * sinc((M_PI / LANCZOS_RADIUS) * x); } } +// The weight function can be expensive to compute over and over again +// (which will happen during e.g. a zoom), but it is also easy to interpolate +// linearly. We compute the right half of the function (in the range of +// 0..LANCZOS_RADIUS), with two guard elements for easier interpolation, and +// linearly interpolate to get our function. +// +// We want to scale the table so that the maximum error is always smaller +// than 1e-6. As per http://www-solar.mcs.st-andrews.ac.uk/~clare/Lectures/num-analysis/Numan_chap3.pdf, +// the error for interpolating a function linearly between points [a,b] is +// +// e = 1/2 (x-a)(x-b) f''(u_x) +// +// for some point u_x in [a,b] (where f(x) is our Lanczos function; we're +// assuming LANCZOS_RADIUS=3 from here on). Obviously this is bounded by +// f''(x) over the entire range. Numeric optimization shows the maximum of +// |f''(x)| to be in x=1.09369819474562880, with the value 2.40067758733152381. +// So if the steps between consecutive values are called d, we get +// +// |e| <= 1/2 (d/2)^2 2.4007 +// |e| <= 0.1367 d^2 +// +// Solve for e = 1e-6 yields a step size of 0.0027, which to cover the range +// 0..3 needs 1109 steps. We round up to the next power of two, just to be sure. +// +// You need to call lanczos_table_init_done before the first call to +// lanczos_weight_cached. +#define LANCZOS_TABLE_SIZE 2048 +bool lanczos_table_init_done = false; +float lanczos_table[LANCZOS_TABLE_SIZE + 2]; + +void init_lanczos_table() +{ + for (unsigned i = 0; i < LANCZOS_TABLE_SIZE + 2; ++i) { + lanczos_table[i] = lanczos_weight(float(i) * (LANCZOS_RADIUS / LANCZOS_TABLE_SIZE)); + } + lanczos_table_init_done = true; +} + +float lanczos_weight_cached(float x) +{ + x = fabs(x); + if (x > LANCZOS_RADIUS) { + return 0.0f; + } + float table_pos = x * (LANCZOS_TABLE_SIZE / LANCZOS_RADIUS); + int table_pos_int = int(table_pos); // Truncate towards zero. + float table_pos_frac = table_pos - table_pos_int; + assert(table_pos < LANCZOS_TABLE_SIZE + 2); + return lanczos_table[table_pos_int] + + table_pos_frac * (lanczos_table[table_pos_int + 1] - lanczos_table[table_pos_int]); +} + // Euclid's algorithm, from Wikipedia. unsigned gcd(unsigned a, unsigned b) { @@ -138,13 +192,13 @@ template void normalize_sum(Tap* vals, unsigned num) { for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) { - double sum = 0.0; + float sum = 0.0; for (unsigned i = 0; i < num; ++i) { - sum += to_fp64(vals[i].weight); + sum += to_fp32(vals[i].weight); } - double inv_sum = 1.0 / sum; + float inv_sum = 1.0 / sum; for (unsigned i = 0; i < num; ++i) { - vals[i].weight = from_fp64(to_fp64(vals[i].weight) * inv_sum); + vals[i].weight = from_fp32(to_fp32(vals[i].weight) * inv_sum); } } } @@ -201,8 +255,8 @@ double compute_sum_sq_error(const Tap* weights, unsigned num_weights, // Find the effective range of the bilinear-optimized kernel. // Due to rounding of the positions, this is not necessarily the same // as the intended range (ie., the range of the original weights). - int lower_pos = int(floor(to_fp64(bilinear_weights[0].pos) * size - 0.5)); - int upper_pos = int(ceil(to_fp64(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5)) + 2; + int lower_pos = int(floor(to_fp32(bilinear_weights[0].pos) * size - 0.5)); + int upper_pos = int(ceil(to_fp32(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5)) + 2; lower_pos = min(lower_pos, lrintf(weights[0].pos * size - 0.5)); upper_pos = max(upper_pos, lrintf(weights[num_weights - 1].pos * size - 0.5) + 1); @@ -213,7 +267,7 @@ double compute_sum_sq_error(const Tap* weights, unsigned num_weights, // Now find the effective weights that result from this sampling. for (unsigned i = 0; i < num_bilinear_weights; ++i) { - const float pixel_pos = to_fp64(bilinear_weights[i].pos) * size - 0.5f; + const float pixel_pos = to_fp32(bilinear_weights[i].pos) * size - 0.5f; const int x0 = int(floor(pixel_pos)) - lower_pos; const int x1 = x0 + 1; const float f = lrintf((pixel_pos - (x0 + lower_pos)) / movit_texel_subpixel_precision) * movit_texel_subpixel_precision; @@ -223,8 +277,8 @@ double compute_sum_sq_error(const Tap* weights, unsigned num_weights, assert(x0 < upper_pos - lower_pos); assert(x1 < upper_pos - lower_pos); - effective_weights[x0] += to_fp64(bilinear_weights[i].weight) * (1.0 - f); - effective_weights[x1] += to_fp64(bilinear_weights[i].weight) * f; + effective_weights[x0] += to_fp32(bilinear_weights[i].weight) * (1.0 - f); + effective_weights[x1] += to_fp32(bilinear_weights[i].weight) * f; } // Subtract the desired weights to get the error. @@ -397,7 +451,7 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent) register_float("offset", &offset); register_float("zoom", &zoom); register_uniform_sampler2d("sample_tex", &uniform_sample_tex); - register_uniform_int("num_samples", &uniform_num_samples); // FIXME: What about GLSL pre-1.30? + register_uniform_int("num_samples", &uniform_num_samples); register_uniform_float("num_loops", &uniform_num_loops); register_uniform_float("slice_height", &uniform_slice_height); register_uniform_float("sample_x_scale", &uniform_sample_x_scale); @@ -405,6 +459,12 @@ SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent) register_uniform_float("whole_pixel_offset", &uniform_whole_pixel_offset); glGenTextures(1, &texnum); + + if (!lanczos_table_init_done) { + // Could in theory race between two threads if we are unlucky, + // but that is harmless, since they'll write the same data. + init_lanczos_table(); + } } SingleResamplePassEffect::~SingleResamplePassEffect() @@ -531,7 +591,7 @@ void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const str // Now sample pixels on each side around that point. for (int i = 0; i < src_samples; ++i) { int src_y = base_src_y + i - int_radius; - float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y - subpixel_offset), LANCZOS_RADIUS); + float weight = lanczos_weight_cached(radius_scaling_factor * (src_y - center_src_y - subpixel_offset)); weights[y * src_samples + i].weight = weight * radius_scaling_factor; weights[y * src_samples + i].pos = (src_y + 0.5) / float(src_size); } @@ -657,10 +717,12 @@ void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const strin // We specifically do not want mipmaps on the input texture; // they break minification. Node *self = chain->find_node_for_effect(this); - glActiveTexture(chain->get_input_sampler(self, 0)); - check_error(); - glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); - check_error(); + if (chain->has_input_sampler(self, 0)) { + glActiveTexture(chain->get_input_sampler(self, 0)); + check_error(); + glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); + check_error(); + } } } // namespace movit