1 // Three-lobed Lanczos, the most common choice.
2 #define LANCZOS_RADIUS 3.0
10 #include <Eigen/Sparse>
11 #include <Eigen/SparseQR>
12 #include <Eigen/OrderingMethods>
14 #include "effect_chain.h"
15 #include "effect_util.h"
18 #include "resample_effect.h"
21 using namespace Eigen;
37 return 1.0f - fabs(x);
43 float lanczos_weight(float x, float a)
48 return sinc(M_PI * x) * sinc(M_PI * x / a);
52 // Euclid's algorithm, from Wikipedia.
53 unsigned gcd(unsigned a, unsigned b)
63 template<class DestFloat>
64 unsigned combine_samples(const Tap<float> *src, Tap<DestFloat> *dst, unsigned src_size, unsigned num_src_samples, unsigned max_samples_saved)
66 unsigned num_samples_saved = 0;
67 for (unsigned i = 0, j = 0; i < num_src_samples; ++i, ++j) {
68 // Copy the sample directly; it will be overwritten later if we can combine.
70 dst[j].weight = convert_float<float, DestFloat>(src[i].weight);
71 dst[j].pos = convert_float<float, DestFloat>(src[i].pos);
74 if (i == num_src_samples - 1) {
75 // Last sample; cannot combine.
78 assert(num_samples_saved <= max_samples_saved);
79 if (num_samples_saved == max_samples_saved) {
80 // We could maybe save more here, but other rows can't, so don't bother.
84 float w1 = src[i].weight;
85 float w2 = src[i + 1].weight;
87 // Differing signs; cannot combine.
91 float pos1 = src[i].pos;
92 float pos2 = src[i + 1].pos;
95 fp16_int_t pos, total_weight;
97 combine_two_samples(w1, w2, pos1, pos2, src_size, &pos, &total_weight, &sum_sq_error);
99 // If the interpolation error is larger than that of about sqrt(2) of
100 // a level at 8-bit precision, don't combine. (You'd think 1.0 was enough,
101 // but since the artifacts are not really random, they can get quite
102 // visible. On the other hand, going to 0.25f, I can see no change at
103 // all with 8-bit output, so it would not seem to be worth it.)
104 if (sum_sq_error > 0.5f / (255.0f * 255.0f)) {
108 // OK, we can combine this and the next sample.
110 dst[j].weight = total_weight;
114 ++i; // Skip the next sample.
117 return num_samples_saved;
120 // Normalize so that the sum becomes one. Note that we do it twice;
121 // this sometimes helps a tiny little bit when we have many samples.
123 void normalize_sum(Tap<T>* vals, unsigned num)
125 for (int normalize_pass = 0; normalize_pass < 2; ++normalize_pass) {
127 for (unsigned i = 0; i < num; ++i) {
128 sum += to_fp64(vals[i].weight);
130 for (unsigned i = 0; i < num; ++i) {
131 vals[i].weight = from_fp64<T>(to_fp64(vals[i].weight) / sum);
136 // Make use of the bilinear filtering in the GPU to reduce the number of samples
137 // we need to make. This is a bit more complex than BlurEffect since we cannot combine
138 // two neighboring samples if their weights have differing signs, so we first need to
139 // figure out the maximum number of samples. Then, we downconvert all the weights to
140 // that number -- we could have gone for a variable-length system, but this is simpler,
141 // and the gains would probably be offset by the extra cost of checking when to stop.
143 // The greedy strategy for combining samples is optimal.
144 template<class DestFloat>
145 unsigned combine_many_samples(const Tap<float> *weights, unsigned src_size, unsigned src_samples, unsigned dst_samples, Tap<DestFloat> **bilinear_weights)
147 int src_bilinear_samples = 0;
148 for (unsigned y = 0; y < dst_samples; ++y) {
149 unsigned num_samples_saved = combine_samples<DestFloat>(weights + y * src_samples, NULL, src_size, src_samples, UINT_MAX);
150 src_bilinear_samples = max<int>(src_bilinear_samples, src_samples - num_samples_saved);
153 // Now that we know the right width, actually combine the samples.
154 *bilinear_weights = new Tap<DestFloat>[dst_samples * src_bilinear_samples];
155 for (unsigned y = 0; y < dst_samples; ++y) {
156 Tap<DestFloat> *bilinear_weights_ptr = *bilinear_weights + y * src_bilinear_samples;
157 unsigned num_samples_saved = combine_samples(
158 weights + y * src_samples,
159 bilinear_weights_ptr,
162 src_samples - src_bilinear_samples);
163 assert(int(src_samples) - int(num_samples_saved) == src_bilinear_samples);
164 normalize_sum(bilinear_weights_ptr, src_bilinear_samples);
166 return src_bilinear_samples;
169 // Compute the sum of squared errors between the ideal weights (which are
170 // assumed to fall exactly on pixel centers) and the weights that result
171 // from sampling at <bilinear_weights>. The primary reason for the difference
172 // is inaccuracy in the sampling positions, both due to limited precision
173 // in storing them (already inherent in sending them in as fp16_int_t)
174 // and in subtexel sampling precision (which we calculate in this function).
176 double compute_sum_sq_error(const Tap<float>* weights, unsigned num_weights,
177 const Tap<T>* bilinear_weights, unsigned num_bilinear_weights,
180 // Find the effective range of the bilinear-optimized kernel.
181 // Due to rounding of the positions, this is not necessarily the same
182 // as the intended range (ie., the range of the original weights).
183 int lower_pos = int(floor(to_fp64(bilinear_weights[0].pos) * size - 0.5));
184 int upper_pos = int(ceil(to_fp64(bilinear_weights[num_bilinear_weights - 1].pos) * size - 0.5)) + 2;
185 lower_pos = min<int>(lower_pos, lrintf(weights[0].pos * size - 0.5));
186 upper_pos = max<int>(upper_pos, lrintf(weights[num_weights - 1].pos * size - 0.5));
188 float* effective_weights = new float[upper_pos - lower_pos];
189 for (int i = 0; i < upper_pos - lower_pos; ++i) {
190 effective_weights[i] = 0.0f;
193 // Now find the effective weights that result from this sampling.
194 for (unsigned i = 0; i < num_bilinear_weights; ++i) {
195 const float pixel_pos = to_fp64(bilinear_weights[i].pos) * size - 0.5f;
196 const int x0 = int(floor(pixel_pos)) - lower_pos;
197 const int x1 = x0 + 1;
198 const float f = lrintf((pixel_pos - (x0 + lower_pos)) / movit_texel_subpixel_precision) * movit_texel_subpixel_precision;
202 assert(x0 < upper_pos - lower_pos);
203 assert(x1 < upper_pos - lower_pos);
205 effective_weights[x0] += to_fp64(bilinear_weights[i].weight) * (1.0 - f);
206 effective_weights[x1] += to_fp64(bilinear_weights[i].weight) * f;
209 // Subtract the desired weights to get the error.
210 for (unsigned i = 0; i < num_weights; ++i) {
211 const int x = lrintf(weights[i].pos * size - 0.5f) - lower_pos;
213 assert(x < upper_pos - lower_pos);
215 effective_weights[x] -= weights[i].weight;
218 double sum_sq_error = 0.0;
219 for (unsigned i = 0; i < num_weights; ++i) {
220 sum_sq_error += effective_weights[i] * effective_weights[i];
223 delete[] effective_weights;
227 // Given a predefined, fixed set of bilinear weight positions, try to optimize
228 // their weights through some linear algebra. This can do a better job than
229 // the weight calculation in combine_samples() because it can look at the entire
230 // picture (an effective weight can sometimes be affected by multiple samples).
231 // It will also optimize weights for non-combined samples, which is useful when
232 // a sample happens in-between texels for numerical reasons.
234 // The math goes as follows: The desired result is a weighted sum, where the
235 // weights are the coefficients in <weights>:
237 // y = sum(c_j x_j, j)
239 // We try to approximate this by a different set of coefficients, which have
240 // weights d_i and are placed at some fraction to the right of a source texel x_j.
241 // This means it will influence two texels (x_j and x_{j+1}); generalizing this,
242 // let us define that w_ij means the amount texel <j> influences bilinear weight
243 // <i> (keeping in mind that w_ij = 0 for all but at most two different j).
244 // This means the actually computed result is:
246 // y' = sum(d_i w_ij x_j, j)
248 // We assume w_ij fixed and wish to find {d_i} so that y' gets as close to y
249 // as possible. Specifically, let us consider the sum of squred errors of the
252 // ε² = sum((sum( d_i w_ij, i ) - c_j)², j)
254 // The standard trick, which also applies just fine here, is to differentiate
255 // the error with respect to each variable we wish to optimize, and set each
256 // such expression to zero. Solving this equation set (which we can do efficiently
257 // by letting Eigen invert a sparse matrix for us) yields the minimum possible
258 // error. To see the form each such equation takes, pick any value k and
259 // differentiate the expression by d_k:
261 // ∂(ε²)/∂(d_k) = sum(2(sum( d_i w_ij, i ) - c_j) w_kj, j)
263 // Setting this expression equal to zero, dropping the irrelevant factor 2 and
264 // rearranging yields:
266 // sum(w_kj sum( d_i w_ij, i ), j) = sum(w_kj c_j, j)
268 // where again, we remember where the sums over j are over at most two elements,
269 // since w_ij is nonzero for at most two values of j.
271 void optimize_sum_sq_error(const Tap<float>* weights, unsigned num_weights,
272 Tap<T>* bilinear_weights, unsigned num_bilinear_weights,
275 // Find the range of the desired weights.
276 int c_lower_pos = lrintf(weights[0].pos * size - 0.5);
277 int c_upper_pos = lrintf(weights[num_weights - 1].pos * size - 0.5) + 1;
279 SparseMatrix<float> A(num_bilinear_weights, num_bilinear_weights);
280 SparseVector<float> b(num_bilinear_weights);
282 // Convert each bilinear weight to the (x, frac) form for less junk in the code below.
283 int* pos = new int[num_bilinear_weights];
284 float* fracs = new float[num_bilinear_weights];
285 for (unsigned i = 0; i < num_bilinear_weights; ++i) {
286 const float pixel_pos = to_fp64(bilinear_weights[i].pos) * size - 0.5f;
287 const float f = pixel_pos - floor(pixel_pos);
288 pos[i] = int(floor(pixel_pos));
289 fracs[i] = lrintf(f / movit_texel_subpixel_precision) * movit_texel_subpixel_precision;
292 // The index ordering is a bit unusual to fit better with the
293 // notation in the derivation above.
294 for (unsigned k = 0; k < num_bilinear_weights; ++k) {
295 for (int j = pos[k]; j <= pos[k] + 1; ++j) {
296 const float f_kj = (j == pos[k]) ? (1.0f - fracs[k]) : fracs[k];
297 for (unsigned i = 0; i < num_bilinear_weights; ++i) {
300 f_ij = 1.0f - fracs[i];
301 } else if (j == pos[i] + 1) {
307 A.coeffRef(i, k) += f_kj * f_ij;
310 if (j >= c_lower_pos && j < c_upper_pos) {
311 c_j = weights[j - c_lower_pos].weight;
315 b.coeffRef(k) += f_kj * c_j;
322 SparseQR<SparseMatrix<float>, COLAMDOrdering<int> > qr(A);
323 assert(qr.info() == Success);
324 SparseMatrix<float> new_weights = qr.solve(b);
325 assert(qr.info() == Success);
327 for (unsigned i = 0; i < num_bilinear_weights; ++i) {
328 bilinear_weights[i].weight = from_fp64<T>(new_weights.coeff(i, 0));
330 normalize_sum(bilinear_weights, num_bilinear_weights);
335 ResampleEffect::ResampleEffect()
338 offset_x(0.0f), offset_y(0.0f),
339 zoom_x(1.0f), zoom_y(1.0f),
340 zoom_center_x(0.5f), zoom_center_y(0.5f)
342 register_int("width", &output_width);
343 register_int("height", &output_height);
345 // The first blur pass will forward resolution information to us.
346 hpass = new SingleResamplePassEffect(this);
347 CHECK(hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL));
348 vpass = new SingleResamplePassEffect(NULL);
349 CHECK(vpass->set_int("direction", SingleResamplePassEffect::VERTICAL));
354 void ResampleEffect::rewrite_graph(EffectChain *graph, Node *self)
356 Node *hpass_node = graph->add_node(hpass);
357 Node *vpass_node = graph->add_node(vpass);
358 graph->connect_nodes(hpass_node, vpass_node);
359 graph->replace_receiver(self, hpass_node);
360 graph->replace_sender(self, vpass_node);
361 self->disabled = true;
364 // We get this information forwarded from the first blur pass,
365 // since we are not part of the chain ourselves.
366 void ResampleEffect::inform_input_size(unsigned input_num, unsigned width, unsigned height)
368 assert(input_num == 0);
372 input_height = height;
376 void ResampleEffect::update_size()
379 ok |= hpass->set_int("input_width", input_width);
380 ok |= hpass->set_int("input_height", input_height);
381 ok |= hpass->set_int("output_width", output_width);
382 ok |= hpass->set_int("output_height", input_height);
384 ok |= vpass->set_int("input_width", output_width);
385 ok |= vpass->set_int("input_height", input_height);
386 ok |= vpass->set_int("output_width", output_width);
387 ok |= vpass->set_int("output_height", output_height);
391 // The offset added due to zoom may have changed with the size.
392 update_offset_and_zoom();
395 void ResampleEffect::update_offset_and_zoom()
399 // Zoom from the right origin. (zoom_center is given in normalized coordinates,
401 float extra_offset_x = zoom_center_x * (1.0f - 1.0f / zoom_x) * input_width;
402 float extra_offset_y = (1.0f - zoom_center_y) * (1.0f - 1.0f / zoom_y) * input_height;
404 ok |= hpass->set_float("offset", extra_offset_x + offset_x);
405 ok |= vpass->set_float("offset", extra_offset_y - offset_y); // Compensate for the bottom-left origin.
406 ok |= hpass->set_float("zoom", zoom_x);
407 ok |= vpass->set_float("zoom", zoom_y);
412 bool ResampleEffect::set_float(const string &key, float value) {
413 if (key == "width") {
414 output_width = value;
418 if (key == "height") {
419 output_height = value;
425 update_offset_and_zoom();
430 update_offset_and_zoom();
433 if (key == "zoom_x") {
438 update_offset_and_zoom();
441 if (key == "zoom_y") {
446 update_offset_and_zoom();
449 if (key == "zoom_center_x") {
450 zoom_center_x = value;
451 update_offset_and_zoom();
454 if (key == "zoom_center_y") {
455 zoom_center_y = value;
456 update_offset_and_zoom();
462 SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
464 direction(HORIZONTAL),
469 last_input_width(-1),
470 last_input_height(-1),
471 last_output_width(-1),
472 last_output_height(-1),
473 last_offset(0.0 / 0.0), // NaN.
474 last_zoom(0.0 / 0.0) // NaN.
476 register_int("direction", (int *)&direction);
477 register_int("input_width", &input_width);
478 register_int("input_height", &input_height);
479 register_int("output_width", &output_width);
480 register_int("output_height", &output_height);
481 register_float("offset", &offset);
482 register_float("zoom", &zoom);
484 glGenTextures(1, &texnum);
487 SingleResamplePassEffect::~SingleResamplePassEffect()
489 glDeleteTextures(1, &texnum);
492 string SingleResamplePassEffect::output_fragment_shader()
495 sprintf(buf, "#define DIRECTION_VERTICAL %d\n", (direction == VERTICAL));
496 return buf + read_file("resample_effect.frag");
499 // Using vertical scaling as an example:
501 // Generally out[y] = w0 * in[yi] + w1 * in[yi + 1] + w2 * in[yi + 2] + ...
503 // Obviously, yi will depend on y (in a not-quite-linear way), but so will
504 // the weights w0, w1, w2, etc.. The easiest way of doing this is to encode,
505 // for each sample, the weight and the yi value, e.g. <yi, w0>, <yi + 1, w1>,
506 // and so on. For each y, we encode these along the x-axis (since that is spare),
507 // so out[0] will read from parameters <x,y> = <0,0>, <1,0>, <2,0> and so on.
509 // For horizontal scaling, we fill in the exact same texture;
510 // the shader just interprets it differently.
511 void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
513 unsigned src_size, dst_size;
514 if (direction == SingleResamplePassEffect::HORIZONTAL) {
515 assert(input_height == output_height);
516 src_size = input_width;
517 dst_size = output_width;
518 } else if (direction == SingleResamplePassEffect::VERTICAL) {
519 assert(input_width == output_width);
520 src_size = input_height;
521 dst_size = output_height;
526 // For many resamplings (e.g. 640 -> 1280), we will end up with the same
527 // set of samples over and over again in a loop. Thus, we can compute only
528 // the first such loop, and then ask the card to repeat the texture for us.
529 // This is both easier on the texture cache and lowers our CPU cost for
530 // generating the kernel somewhat.
531 float scaling_factor;
532 if (fabs(zoom - 1.0f) < 1e-6) {
533 num_loops = gcd(src_size, dst_size);
534 scaling_factor = float(dst_size) / float(src_size);
536 // If zooming is enabled (ie., zoom != 1), we turn off the looping.
537 // We _could_ perhaps do it for rational zoom levels (especially
538 // things like 2:1), but it doesn't seem to be worth it, given that
539 // the most common use case would seem to be varying the zoom
540 // from frame to frame.
542 scaling_factor = zoom * float(dst_size) / float(src_size);
544 slice_height = 1.0f / num_loops;
545 unsigned dst_samples = dst_size / num_loops;
547 // Sample the kernel in the right place. A diagram with a triangular kernel
548 // (corresponding to linear filtering, and obviously with radius 1)
549 // for easier ASCII art drawing:
555 // x---x---x x x---x---x---x
557 // Scaling up (in this case, 2x) means sampling more densely:
563 // x-x-x-x-x-x x x x-x-x-x-x-x-x-x
565 // When scaling up, any destination pixel will only be influenced by a few
566 // (in this case, two) neighboring pixels, and more importantly, the number
567 // will not be influenced by the scaling factor. (Note, however, that the
568 // pixel centers have moved, due to OpenGL's center-pixel convention.)
569 // The only thing that changes is the weights themselves, as the sampling
570 // points are at different distances from the original pixels.
572 // Scaling down is a different story:
578 // --x------ x --x-------x--
580 // Again, the pixel centers have moved in a maybe unintuitive fashion,
581 // although when you consider that there are multiple source pixels around,
582 // it's not so bad as at first look:
588 // --x-------x-------x-------x--
590 // As you can see, the new pixels become averages of the two neighboring old
591 // ones (the situation for Lanczos is of course more complex).
593 // Anyhow, in this case we clearly need to look at more source pixels
594 // to compute the destination pixel, and how many depend on the scaling factor.
595 // Thus, the kernel width will vary with how much we scale.
596 float radius_scaling_factor = min(scaling_factor, 1.0f);
597 int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
598 int src_samples = int_radius * 2 + 1;
599 Tap<float> *weights = new Tap<float>[dst_samples * src_samples];
600 float subpixel_offset = offset - lrintf(offset); // The part not covered by whole_pixel_offset.
601 assert(subpixel_offset >= -0.5f && subpixel_offset <= 0.5f);
602 for (unsigned y = 0; y < dst_samples; ++y) {
603 // Find the point around which we want to sample the source image,
604 // compensating for differing pixel centers as the scale changes.
605 float center_src_y = (y + 0.5f) / scaling_factor - 0.5f;
606 int base_src_y = lrintf(center_src_y);
608 // Now sample <int_radius> pixels on each side around that point.
609 for (int i = 0; i < src_samples; ++i) {
610 int src_y = base_src_y + i - int_radius;
611 float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y - subpixel_offset), LANCZOS_RADIUS);
612 weights[y * src_samples + i].weight = weight * radius_scaling_factor;
613 weights[y * src_samples + i].pos = (src_y + 0.5) / float(src_size);
617 // Now make use of the bilinear filtering in the GPU to reduce the number of samples
618 // we need to make. Try fp16 first; if it's not accurate enough, we go to fp32.
619 Tap<fp16_int_t> *bilinear_weights_fp16;
620 src_bilinear_samples = combine_many_samples(weights, src_size, src_samples, dst_samples, &bilinear_weights_fp16);
621 Tap<float> *bilinear_weights_fp32 = NULL;
622 bool fallback_to_fp32 = false;
623 double max_sum_sq_error_fp16 = 0.0;
624 for (unsigned y = 0; y < dst_samples; ++y) {
625 optimize_sum_sq_error(
626 weights + y * src_samples, src_samples,
627 bilinear_weights_fp16 + y * src_bilinear_samples, src_bilinear_samples,
629 double sum_sq_error_fp16 = compute_sum_sq_error(
630 weights + y * src_samples, src_samples,
631 bilinear_weights_fp16 + y * src_bilinear_samples, src_bilinear_samples,
633 max_sum_sq_error_fp16 = std::max(max_sum_sq_error_fp16, sum_sq_error_fp16);
636 // Our tolerance level for total error is a bit higher than the one for invididual
637 // samples, since one would assume overall errors in the shape don't matter as much.
638 if (max_sum_sq_error_fp16 > 2.0f / (255.0f * 255.0f)) {
639 fallback_to_fp32 = true;
640 src_bilinear_samples = combine_many_samples(weights, src_size, src_samples, dst_samples, &bilinear_weights_fp32);
641 for (unsigned y = 0; y < dst_samples; ++y) {
642 optimize_sum_sq_error(
643 weights + y * src_samples, src_samples,
644 bilinear_weights_fp32 + y * src_bilinear_samples, src_bilinear_samples,
649 // Encode as a two-component texture. Note the GL_REPEAT.
650 glActiveTexture(GL_TEXTURE0 + *sampler_num);
652 glBindTexture(GL_TEXTURE_2D, texnum);
654 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
656 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
658 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
660 if (fallback_to_fp32) {
661 glTexImage2D(GL_TEXTURE_2D, 0, GL_RG32F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_FLOAT, bilinear_weights_fp32);
663 glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_bilinear_samples, dst_samples, 0, GL_RG, GL_HALF_FLOAT, bilinear_weights_fp16);
668 delete[] bilinear_weights_fp16;
669 delete[] bilinear_weights_fp32;
672 void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
674 Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
676 assert(input_width > 0);
677 assert(input_height > 0);
678 assert(output_width > 0);
679 assert(output_height > 0);
681 if (input_width != last_input_width ||
682 input_height != last_input_height ||
683 output_width != last_output_width ||
684 output_height != last_output_height ||
685 offset != last_offset ||
687 update_texture(glsl_program_num, prefix, sampler_num);
688 last_input_width = input_width;
689 last_input_height = input_height;
690 last_output_width = output_width;
691 last_output_height = output_height;
692 last_offset = offset;
696 glActiveTexture(GL_TEXTURE0 + *sampler_num);
698 glBindTexture(GL_TEXTURE_2D, texnum);
701 set_uniform_int(glsl_program_num, prefix, "sample_tex", *sampler_num);
703 set_uniform_int(glsl_program_num, prefix, "num_samples", src_bilinear_samples);
704 set_uniform_float(glsl_program_num, prefix, "num_loops", num_loops);
705 set_uniform_float(glsl_program_num, prefix, "slice_height", slice_height);
707 // Instructions for how to convert integer sample numbers to positions in the weight texture.
708 set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_bilinear_samples);
709 set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_bilinear_samples);
711 float whole_pixel_offset;
712 if (direction == SingleResamplePassEffect::VERTICAL) {
713 whole_pixel_offset = lrintf(offset) / float(input_height);
715 whole_pixel_offset = lrintf(offset) / float(input_width);
717 set_uniform_float(glsl_program_num, prefix, "whole_pixel_offset", whole_pixel_offset);
719 // We specifically do not want mipmaps on the input texture;
720 // they break minification.
721 Node *self = chain->find_node_for_effect(this);
722 glActiveTexture(chain->get_input_sampler(self, 0));
724 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);