git.sesse.net Git - movit/blob - resample_effect.cpp

   1 // Three-lobed Lanczos, the most common choice.
   2 #define LANCZOS_RADIUS 3.0
   3
   4 #include <math.h>
   5 #include <assert.h>
   6
   7 #include "resample_effect.h"
   8 #include "effect_chain.h"
   9 #include "util.h"
  10 #include "opengl.h"
  11
  12 namespace {
  13
  14 float sinc(float x)
  15 {
  16         if (fabs(x) < 1e-6) {
  17                 return 1.0f - fabs(x);
  18         } else {
  19                 return sin(x) / x;
  20         }
  21 }
  22
  23 float lanczos_weight(float x, float a)
  24 {
  25         if (fabs(x) > a) {
  26                 return 0.0f;
  27         } else {
  28                 return sinc(M_PI * x) * sinc(M_PI * x / a);
  29         }
  30 }
  31
  32 }  // namespace
  33
  34 ResampleEffect::ResampleEffect()
  35         : input_width(1280),
  36           input_height(720)
  37 {
  38         register_int("width", &output_width);
  39         register_int("height", &output_height);
  40
  41         // The first blur pass will forward resolution information to us.
  42         hpass = new SingleResamplePassEffect(this);
  43         hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL);
  44         vpass = new SingleResamplePassEffect(NULL);
  45         vpass->set_int("direction", SingleResamplePassEffect::VERTICAL);
  46
  47         update_size();
  48 }
  49
  50 void ResampleEffect::rewrite_graph(EffectChain *graph, Node *self)
  51 {
  52         Node *hpass_node = graph->add_node(hpass);
  53         Node *vpass_node = graph->add_node(vpass);
  54         graph->connect_nodes(hpass_node, vpass_node);
  55         graph->replace_receiver(self, hpass_node);
  56         graph->replace_sender(self, vpass_node);
  57         self->disabled = true;
  58 }
  59
  60 // We get this information forwarded from the first blur pass,
  61 // since we are not part of the chain ourselves.
  62 void ResampleEffect::inform_input_size(unsigned input_num, unsigned width, unsigned height)
  63 {
  64         assert(input_num == 0);
  65         assert(width != 0);
  66         assert(height != 0);
  67         input_width = width;
  68         input_height = height;
  69         update_size();
  70 }
  71
  72 void ResampleEffect::update_size()
  73 {
  74         bool ok = true;
  75         ok |= hpass->set_int("input_width", input_width);
  76         ok |= hpass->set_int("input_height", input_height);
  77         ok |= hpass->set_int("output_width", output_width);
  78         ok |= hpass->set_int("output_height", input_height);
  79
  80         ok |= vpass->set_int("input_width", output_width);
  81         ok |= vpass->set_int("input_height", input_height);
  82         ok |= vpass->set_int("output_width", output_width);
  83         ok |= vpass->set_int("output_height", output_height);
  84
  85         assert(ok);
  86 }
  87
  88 bool ResampleEffect::set_float(const std::string &key, float value) {
  89         if (key == "width") {
  90                 output_width = value;
  91                 update_size();
  92                 return true;
  93         }
  94         if (key == "height") {
  95                 output_height = value;
  96                 update_size();
  97                 return true;
  98         }
  99         return false;
 100 }
 101
 102 SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
 103         : parent(parent),
 104           direction(HORIZONTAL),
 105           input_width(1280),
 106           input_height(720),
 107           last_input_width(-1),
 108           last_input_height(-1),
 109           last_output_width(-1),
 110           last_output_height(-1)
 111 {
 112         register_int("direction", (int *)&direction);
 113         register_int("input_width", &input_width);
 114         register_int("input_height", &input_height);
 115         register_int("output_width", &output_width);
 116         register_int("output_height", &output_height);
 117
 118         glGenTextures(1, &texnum);
 119 }
 120
 121 SingleResamplePassEffect::~SingleResamplePassEffect()
 122 {
 123         glDeleteTextures(1, &texnum);
 124 }
 125
 126 std::string SingleResamplePassEffect::output_fragment_shader()
 127 {
 128         char buf[256];
 129         sprintf(buf, "#define DIRECTION_VERTICAL %d\n", (direction == VERTICAL));
 130         return buf + read_file("resample_effect.frag");
 131 }
 132
 133 // Using vertical scaling as an example:
 134 //
 135 // Generally out[y] = w0 * in[yi] + w1 * in[yi + 1] + w2 * in[yi + 2] + ...
 136 //
 137 // Obviously, yi will depend on y (in a not-quite-linear way), but so will
 138 // the weights w0, w1, w2, etc.. The easiest way of doing this is to encode,
 139 // for each sample, the weight and the yi value, e.g. <yi, w0>, <yi + 1, w1>,
 140 // and so on. For each y, we encode these along the x-axis (since that is spare),
 141 // so out[0] will read from parameters <x,y> = <0,0>, <1,0>, <2,0> and so on.
 142 //
 143 // For horizontal scaling, we fill in the exact same texture;
 144 // the shader just interprets is differently.
 145 //
 146 // TODO: Support optimization of wrapping the sample texture.
 147 // TODO: Support optimization using free linear sampling, like in BlurEffect.
 148 void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
 149 {
 150         unsigned src_size, dst_size;
 151         if (direction == SingleResamplePassEffect::HORIZONTAL) {
 152                 assert(input_height == output_height);
 153                 src_size = input_width;
 154                 dst_size = output_width;
 155         } else if (direction == SingleResamplePassEffect::VERTICAL) {
 156                 assert(input_width == output_width);
 157                 src_size = input_height;
 158                 dst_size = output_height;
 159         } else {
 160                 assert(false);
 161         }
 162
 163         // Sample the kernel in the right place. A diagram with a triangular kernel
 164         // (corresponding to linear filtering, and obviously with radius 1)
 165         // for easier ASCII art drawing:
 166         //
 167         //                *
 168         //               / \                      |
 169         //              /   \                     |
 170         //             /     \                    |
 171         //    x---x---x   x   x---x---x---x
 172         //
 173         // Scaling up (in this case, 2x) means sampling more densely:
 174         //
 175         //                *
 176         //               / \                      |
 177         //              /   \                     |
 178         //             /     \                    |
 179         //   x-x-x-x-x-x x x x-x-x-x-x-x-x-x
 180         //
 181         // When scaling up, any destination pixel will only be influenced by a few
 182         // (in this case, two) neighboring pixels, and more importantly, the number
 183         // will not be influenced by the scaling factor. (Note, however, that the
 184         // pixel centers have moved, due to OpenGL's center-pixel convention.)
 185         // The only thing that changes is the weights themselves, as the sampling
 186         // points are at different distances from the original pixels.
 187         //
 188         // Scaling down is a different story:
 189         //
 190         //                *
 191         //               / \                      |
 192         //              /   \                     |
 193         //             /     \                    |
 194         //    --x------ x     --x-------x--
 195         //
 196         // Again, the pixel centers have moved in a maybe unintuitive fashion,
 197         // although when you consider that there are multiple source pixels around,
 198         // it's not so bad as at first look:
 199         //
 200         //            *   *   *   *
 201         //           / \ / \ / \ / \              |
 202         //          /   X   X   X   \             |
 203         //         /   / \ / \ / \   \            |
 204         //    --x-------x-------x-------x--
 205         //
 206         // As you can see, the new pixels become averages of the two neighboring old
 207         // ones (the situation for Lanczos is of course more complex).
 208         //
 209         // Anyhow, in this case we clearly need to look at more source pixels
 210         // to compute the destination pixel, and how many depend on the scaling factor.
 211         // Thus, the kernel width will vary with how much we scale.
 212         float radius_scaling_factor = std::min(float(dst_size) / float(src_size), 1.0f);
 213         int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
 214         src_samples = int_radius * 2 + 1;
 215         float *weights = new float[dst_size * src_samples * 2];
 216         for (unsigned y = 0; y < dst_size; ++y) {
 217                 // Find the point around which we want to sample the source image,
 218                 // compensating for differing pixel centers as the scale changes.
 219                 float center_src_y = (y + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
 220                 int base_src_y = lrintf(center_src_y);
 221
 222                 // Now sample <int_radius> pixels on each side around that point.
 223                 for (int i = 0; i < src_samples; ++i) {
 224                         int src_y = base_src_y + i - int_radius;
 225                         float weight = lanczos_weight(radius_scaling_factor * (src_y - center_src_y), LANCZOS_RADIUS);
 226                         weights[(y * src_samples + i) * 2 + 0] = weight * radius_scaling_factor;
 227                         weights[(y * src_samples + i) * 2 + 1] = (src_y + 0.5) / float(src_size);
 228                 }
 229         }
 230
 231         // Encode as a two-component texture. Note the GL_REPEAT, which is not relevant
 232         // right now, but will be later.
 233         glActiveTexture(GL_TEXTURE0 + *sampler_num);
 234         check_error();
 235         glBindTexture(GL_TEXTURE_2D, texnum);
 236         check_error();
 237         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 238         check_error();
 239         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 240         check_error();
 241         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 242         check_error();
 243         glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_samples, dst_size, 0, GL_RG, GL_FLOAT, weights);
 244         check_error();
 245
 246         delete[] weights;
 247
 248 }
 249
 250 void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
 251 {
 252         Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
 253
 254         if (input_width != last_input_width ||
 255             input_height != last_input_height ||
 256             output_width != last_output_width ||
 257             output_height != last_output_height) {
 258                 update_texture(glsl_program_num, prefix, sampler_num);
 259                 last_input_width = input_width;
 260                 last_input_height = input_height;
 261                 last_output_width = output_width;
 262                 last_output_height = output_height;
 263         }
 264
 265         glActiveTexture(GL_TEXTURE0 + *sampler_num);
 266         check_error();
 267         glBindTexture(GL_TEXTURE_2D, texnum);
 268         check_error();
 269
 270         set_uniform_int(glsl_program_num, prefix, "sample_tex", *sampler_num);
 271         ++sampler_num;
 272         set_uniform_int(glsl_program_num, prefix, "num_samples", src_samples);
 273
 274         // Instructions for how to convert integer sample numbers to positions in the weight texture.
 275         set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_samples);
 276         set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_samples);
 277
 278         // We specifically do not want mipmaps on the input texture;
 279         // they break minification.
 280         glActiveTexture(GL_TEXTURE0);
 281         check_error();
 282         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 283         check_error();
 284 }