1 // Three-lobed Lanczos, the most common choice.
2 #define LANCZOS_RADIUS 3.0
11 #include "effect_chain.h"
12 #include "effect_util.h"
14 #include "resample_effect.h"
32 return 1.0f - fabs(x);
38 float lanczos_weight(float x, float a)
43 return sinc(M_PI * x) * sinc(M_PI * x / a);
47 // Euclid's algorithm, from Wikipedia.
48 unsigned gcd(unsigned a, unsigned b)
58 unsigned combine_samples(Tap<float> *src, Tap<float> *dst, unsigned src_size, unsigned num_src_samples, unsigned max_samples_saved)
60 unsigned num_samples_saved = 0;
61 for (unsigned i = 0, j = 0; i < num_src_samples; ++i, ++j) {
62 // Copy the sample directly; it will be overwritten later if we can combine.
67 if (i == num_src_samples - 1) {
68 // Last sample; cannot combine.
71 assert(num_samples_saved <= max_samples_saved);
72 if (num_samples_saved == max_samples_saved) {
73 // We could maybe save more here, but other rows can't, so don't bother.
77 float w1 = src[i].weight;
78 float w2 = src[i + 1].weight;
80 // Differing signs; cannot combine.
84 float pos1 = src[i].pos;
85 float pos2 = src[i + 1].pos;
88 float pos, total_weight, sum_sq_error;
89 combine_two_samples(w1, w2, pos1, pos2, src_size, COMBINE_ROUND_TO_FP16, &pos, &total_weight, &sum_sq_error);
91 // If the interpolation error is larger than that of about sqrt(2) of
92 // a level at 8-bit precision, don't combine. (You'd think 1.0 was enough,
93 // but since the artifacts are not really random, they can get quite
94 // visible. On the other hand, going to 0.25f, I can see no change at
95 // all with 8-bit output, so it would not seem to be worth it.)
96 if (sum_sq_error > 0.5f / (256.0f * 256.0f)) {
100 // OK, we can combine this and the next sample.
102 dst[j].weight = total_weight;
106 ++i; // Skip the next sample.
109 return num_samples_saved;
114 ResampleEffect::ResampleEffect()
117 offset_x(0.0f), offset_y(0.0f),
118 zoom_x(1.0f), zoom_y(1.0f),
119 zoom_center_x(0.5f), zoom_center_y(0.5f)
121 register_int("width", &output_width);
122 register_int("height", &output_height);
124 // The first blur pass will forward resolution information to us.
125 hpass = new SingleResamplePassEffect(this);
126 CHECK(hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL));
127 vpass = new SingleResamplePassEffect(NULL);
128 CHECK(vpass->set_int("direction", SingleResamplePassEffect::VERTICAL));
133 void ResampleEffect::rewrite_graph(EffectChain *graph, Node *self)
135 Node *hpass_node = graph->add_node(hpass);
136 Node *vpass_node = graph->add_node(vpass);
137 graph->connect_nodes(hpass_node, vpass_node);
138 graph->replace_receiver(self, hpass_node);
139 graph->replace_sender(self, vpass_node);
140 self->disabled = true;
143 // We get this information forwarded from the first blur pass,
144 // since we are not part of the chain ourselves.
145 void ResampleEffect::inform_input_size(unsigned input_num, unsigned width, unsigned height)
147 assert(input_num == 0);
151 input_height = height;
155 void ResampleEffect::update_size()
158 ok |= hpass->set_int("input_width", input_width);
159 ok |= hpass->set_int("input_height", input_height);
160 ok |= hpass->set_int("output_width", output_width);
161 ok |= hpass->set_int("output_height", input_height);
163 ok |= vpass->set_int("input_width", output_width);
164 ok |= vpass->set_int("input_height", input_height);
165 ok |= vpass->set_int("output_width", output_width);
166 ok |= vpass->set_int("output_height", output_height);
170 // The offset added due to zoom may have changed with the size.
171 update_offset_and_zoom();
174 void ResampleEffect::update_offset_and_zoom()
178 // Zoom from the right origin. (zoom_center is given in normalized coordinates,
180 float extra_offset_x = zoom_center_x * (1.0f - 1.0f / zoom_x) * input_width;
181 float extra_offset_y = (1.0f - zoom_center_y) * (1.0f - 1.0f / zoom_y) * input_height;
183 ok |= hpass->set_float("offset", extra_offset_x + offset_x);
184 ok |= vpass->set_float("offset", extra_offset_y - offset_y); // Compensate for the bottom-left origin.
185 ok |= hpass->set_float("zoom", zoom_x);
186 ok |= vpass->set_float("zoom", zoom_y);
191 bool ResampleEffect::set_float(const string &key, float value) {
192 if (key == "width") {
193 output_width = value;
197 if (key == "height") {
198 output_height = value;
204 update_offset_and_zoom();
209 update_offset_and_zoom();
212 if (key == "zoom_x") {
217 update_offset_and_zoom();
220 if (key == "zoom_y") {
225 update_offset_and_zoom();
228 if (key == "zoom_center_x") {
229 zoom_center_x = value;
230 update_offset_and_zoom();
233 if (key == "zoom_center_y") {
234 zoom_center_y = value;
235 update_offset_and_zoom();
241 SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
243 direction(HORIZONTAL),
248 last_input_width(-1),
249 last_input_height(-1),
250 last_output_width(-1),
251 last_output_height(-1),
252 last_offset(0.0 / 0.0), // NaN.
253 last_zoom(0.0 / 0.0) // NaN.
255 register_int("direction", (int *)&direction);
256 register_int("input_width", &input_width);
257 register_int("input_height", &input_height);
258 register_int("output_width", &output_width);
259 register_int("output_height", &output_height);
260 register_float("offset", &offset);
261 register_float("zoom", &zoom);
263 glGenTextures(1, &texnum);
266 SingleResamplePassEffect::~SingleResamplePassEffect()
268 glDeleteTextures(1, &texnum);
271 string SingleResamplePassEffect::output_fragment_shader()
274 sprintf(buf, "#define DIRECTION_VERTICAL %d\n", (direction == VERTICAL));
275 return buf + read_file("resample_effect.frag");
278 // Using vertical scaling as an example:
280 // Generally out[y] = w0 * in[yi] + w1 * in[yi + 1] + w2 * in[yi + 2] + ...
282 // Obviously, yi will depend on y (in a not-quite-linear way), but so will
283 // the weights w0, w1, w2, etc.. The easiest way of doing this is to encode,
284 // for each sample, the weight and the yi value, e.g. <yi, w0>, <yi + 1, w1>,
285 // and so on. For each y, we encode these along the x-axis (since that is spare),
286 // so out[0] will read from parameters <x,y> = <0,0>, <1,0>, <2,0> and so on.
288 // For horizontal scaling, we fill in the exact same texture;
289 // the shader just interprets it differently.
290 void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
292 unsigned src_size, dst_size;
293 if (direction == SingleResamplePassEffect::HORIZONTAL) {
294 assert(input_height == output_height);
295 src_size = input_width;
296 dst_size = output_width;
297 } else if (direction == SingleResamplePassEffect::VERTICAL) {
298 assert(input_width == output_width);
299 src_size = input_height;
300 dst_size = output_height;
305 // For many resamplings (e.g. 640 -> 1280), we will end up with the same
306 // set of samples over and over again in a loop. Thus, we can compute only
307 // the first such loop, and then ask the card to repeat the texture for us.
308 // This is both easier on the texture cache and lowers our CPU cost for
309 // generating the kernel somewhat.
310 float scaling_factor;
311 if (fabs(zoom - 1.0f) < 1e-6) {
312 num_loops = gcd(src_size, dst_size);
313 scaling_factor = float(dst_size) / float(src_size);
315 // If zooming is enabled (ie., zoom != 1), we turn off the looping.
316 // We _could_ perhaps do it for rational zoom levels (especially
317 // things like 2:1), but it doesn't seem to be worth it, given that
318 // the most common use case would seem to be varying the zoom
319 // from frame to frame.
321 scaling_factor = zoom * float(dst_size) / float(src_size);
323 slice_height = 1.0f / num_loops;
324 unsigned dst_samples = dst_size / num_loops;
326 // Sample the kernel in the right place. A diagram with a triangular kernel
327 // (corresponding to linear filtering, and obviously with radius 1)
328 // for easier ASCII art drawing:
334 // x---x---x x x---x---x---x
336 // Scaling up (in this case, 2x) means sampling more densely:
342 // x-x-x-x-x-x x x x-x-x-x-x-x-x-x
344 // When scaling up, any destination pixel will only be influenced by a few
345 // (in this case, two) neighboring pixels, and more importantly, the number
346 // will not be influenced by the scaling factor. (Note, however, that the
347 // pixel centers have moved, due to OpenGL's center-pixel convention.)
348 // The only thing that changes is the weights themselves, as the sampling
349 // points are at different distances from the original pixels.
351 // Scaling down is a different story:
357 // --x------ x --x-------x--
359 // Again, the pixel centers have moved in a maybe unintuitive fashion,
360 // although when you consider that there are multiple source pixels around,
361 // it's not so bad as at first look:
367 // --x-------x-------x-------x--
369 // As you can see, the new pixels become averages of the two neighboring old
370 // ones (the situation for Lanczos is of course more complex).
372 // Anyhow, in this case we clearly need to look at more source pixels
373 // to compute the destination pixel, and how many depend on the scaling factor.
374 // Thus, the kernel width will vary with how much we scale.
375 float radius_scaling_factor = min(scaling_factor, 1.0f);
376 int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
377 int src_samples = int_radius * 2 + 1;
378 Tap<float> *weights = new Tap<float>[dst_samples * src_samples];
379 float subpixel_offset = offset - lrintf(offset); // The part not covered by whole_pixel_offset.
380 assert(subpixel_offset >= -0.5f && subpixel_offset <= 0.5f);
381 for (unsigned y = 0; y < dst_samples; ++y) {
382 // Find the point around which we want to sample the source image,
383 // compensating for differing pixel centers as the scale changes.
384 float center_src_y = (y + 0.5f) / scaling_factor - 0.5f;
385 int base_src_y = lrintf(center_src_y);
387 // Now sample <int_radius> pixels on each side around that point.
388 for (int i = 0; i < src_samples; ++i) {
389 int src_y = base_src_y + i - int_radius;
390 float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y - subpixel_offset), LANCZOS_RADIUS);
391 weights[y * src_samples + i].weight = weight * radius_scaling_factor;
392 weights[y * src_samples + i].pos = (src_y + 0.5) / float(src_size);
396 // Now make use of the bilinear filtering in the GPU to reduce the number of samples
397 // we need to make. This is a bit more complex than BlurEffect since we cannot combine
398 // two neighboring samples if their weights have differing signs, so we first need to
399 // figure out the maximum number of samples. Then, we downconvert all the weights to
400 // that number -- we could have gone for a variable-length system, but this is simpler,
401 // and the gains would probably be offset by the extra cost of checking when to stop.
403 // The greedy strategy for combining samples is optimal.
404 src_bilinear_samples = 0;
405 for (unsigned y = 0; y < dst_samples; ++y) {
406 unsigned num_samples_saved = combine_samples(weights + y * src_samples, NULL, src_size, src_samples, UINT_MAX);
407 src_bilinear_samples = max<int>(src_bilinear_samples, src_samples - num_samples_saved);
410 // Now that we know the right width, actually combine the samples.
411 Tap<float> *bilinear_weights = new Tap<float>[dst_samples * src_bilinear_samples];
412 Tap<fp16_int_t> *bilinear_weights_fp16 = new Tap<fp16_int_t>[dst_samples * src_bilinear_samples];
413 for (unsigned y = 0; y < dst_samples; ++y) {
414 Tap<float> *bilinear_weights_ptr = bilinear_weights + y * src_bilinear_samples;
415 Tap<fp16_int_t> *bilinear_weights_fp16_ptr = bilinear_weights_fp16 + y * src_bilinear_samples;
416 unsigned num_samples_saved = combine_samples(
417 weights + y * src_samples,
418 bilinear_weights_ptr,
421 src_samples - src_bilinear_samples);
422 assert(int(src_samples) - int(num_samples_saved) == src_bilinear_samples);
425 for (int i = 0; i < src_bilinear_samples; ++i) {
426 bilinear_weights_fp16_ptr[i].weight = fp64_to_fp16(bilinear_weights_ptr[i].weight);
427 bilinear_weights_fp16_ptr[i].pos = fp64_to_fp16(bilinear_weights_ptr[i].pos);
430 // Normalize so that the sum becomes one. Note that we do it twice;
431 // this sometimes helps a tiny little bit when we have many samples.
432 for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) {
434 for (int i = 0; i < src_bilinear_samples; ++i) {
435 sum += fp16_to_fp64(bilinear_weights_fp16_ptr[i].weight);
437 for (int i = 0; i < src_bilinear_samples; ++i) {
438 bilinear_weights_fp16_ptr[i].weight = fp64_to_fp16(
439 fp16_to_fp64(bilinear_weights_fp16_ptr[i].weight) / sum);
444 // Encode as a two-component texture. Note the GL_REPEAT.
445 glActiveTexture(GL_TEXTURE0 + *sampler_num);
447 glBindTexture(GL_TEXTURE_2D, texnum);
449 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
451 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
453 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
455 glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_HALF_FLOAT, bilinear_weights_fp16);
459 delete[] bilinear_weights;
460 delete[] bilinear_weights_fp16;
463 void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
465 Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
467 assert(input_width > 0);
468 assert(input_height > 0);
469 assert(output_width > 0);
470 assert(output_height > 0);
472 if (input_width != last_input_width ||
473 input_height != last_input_height ||
474 output_width != last_output_width ||
475 output_height != last_output_height ||
476 offset != last_offset ||
478 update_texture(glsl_program_num, prefix, sampler_num);
479 last_input_width = input_width;
480 last_input_height = input_height;
481 last_output_width = output_width;
482 last_output_height = output_height;
483 last_offset = offset;
487 glActiveTexture(GL_TEXTURE0 + *sampler_num);
489 glBindTexture(GL_TEXTURE_2D, texnum);
492 set_uniform_int(glsl_program_num, prefix, "sample_tex", *sampler_num);
494 set_uniform_int(glsl_program_num, prefix, "num_samples", src_bilinear_samples);
495 set_uniform_float(glsl_program_num, prefix, "num_loops", num_loops);
496 set_uniform_float(glsl_program_num, prefix, "slice_height", slice_height);
498 // Instructions for how to convert integer sample numbers to positions in the weight texture.
499 set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_bilinear_samples);
500 set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_bilinear_samples);
502 float whole_pixel_offset;
503 if (direction == SingleResamplePassEffect::VERTICAL) {
504 whole_pixel_offset = lrintf(offset) / float(input_height);
506 whole_pixel_offset = lrintf(offset) / float(input_width);
508 set_uniform_float(glsl_program_num, prefix, "whole_pixel_offset", whole_pixel_offset);
510 // We specifically do not want mipmaps on the input texture;
511 // they break minification.
512 Node *self = chain->find_node_for_effect(this);
513 glActiveTexture(chain->get_input_sampler(self, 0));
515 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);