--- /dev/null
+// Three-lobed Lanczos, the most common choice.
+#define LANCZOS_RADIUS 3.0
+
+#include <math.h>
+#include <assert.h>
+
+#include "resample_effect.h"
+#include "effect_chain.h"
+#include "util.h"
+#include "opengl.h"
+
+namespace {
+
+float sinc(float x)
+{
+ if (fabs(x) < 1e-6) {
+ return 1.0f - fabs(x);
+ } else {
+ return sin(x) / x;
+ }
+}
+
+float lanczos_weight(float x, float a)
+{
+ if (fabs(x) > a) {
+ return 0.0f;
+ } else {
+ return sinc(M_PI * x) * sinc(M_PI * x / a);
+ }
+}
+
+} // namespace
+
+ResampleEffect::ResampleEffect()
+ : input_width(1280),
+ input_height(720)
+{
+ register_int("width", &output_width);
+ register_int("height", &output_height);
+
+ // The first blur pass will forward resolution information to us.
+ hpass = new SingleResamplePassEffect(this);
+ hpass->set_int("direction", SingleResamplePassEffect::HORIZONTAL);
+ vpass = new SingleResamplePassEffect(NULL);
+ vpass->set_int("direction", SingleResamplePassEffect::VERTICAL);
+
+ update_size();
+}
+
+void ResampleEffect::rewrite_graph(EffectChain *graph, Node *self)
+{
+ Node *hpass_node = graph->add_node(hpass);
+ Node *vpass_node = graph->add_node(vpass);
+ graph->connect_nodes(hpass_node, vpass_node);
+ graph->replace_receiver(self, hpass_node);
+ graph->replace_sender(self, vpass_node);
+ self->disabled = true;
+}
+
+// We get this information forwarded from the first blur pass,
+// since we are not part of the chain ourselves.
+void ResampleEffect::inform_input_size(unsigned input_num, unsigned width, unsigned height)
+{
+ assert(input_num == 0);
+ assert(width != 0);
+ assert(height != 0);
+ input_width = width;
+ input_height = height;
+ update_size();
+}
+
+void ResampleEffect::update_size()
+{
+ bool ok = true;
+ ok |= hpass->set_int("input_width", input_width);
+ ok |= hpass->set_int("input_height", input_height);
+ ok |= hpass->set_int("output_width", output_width);
+ ok |= hpass->set_int("output_height", input_height);
+
+ ok |= vpass->set_int("input_width", output_width);
+ ok |= vpass->set_int("input_height", input_height);
+ ok |= vpass->set_int("output_width", output_width);
+ ok |= vpass->set_int("output_height", output_height);
+
+ assert(ok);
+}
+
+bool ResampleEffect::set_float(const std::string &key, float value) {
+ if (key == "width") {
+ output_width = value;
+ update_size();
+ return true;
+ }
+ if (key == "height") {
+ output_height = value;
+ update_size();
+ return true;
+ }
+ return false;
+}
+
+SingleResamplePassEffect::SingleResamplePassEffect(ResampleEffect *parent)
+ : parent(parent),
+ direction(HORIZONTAL),
+ input_width(1280),
+ input_height(720),
+ last_input_width(-1),
+ last_input_height(-1),
+ last_output_width(-1),
+ last_output_height(-1)
+{
+ register_int("direction", (int *)&direction);
+ register_int("input_width", &input_width);
+ register_int("input_height", &input_height);
+ register_int("output_width", &output_width);
+ register_int("output_height", &output_height);
+
+ glGenTextures(1, &texnum);
+}
+
+SingleResamplePassEffect::~SingleResamplePassEffect()
+{
+ glDeleteTextures(1, &texnum);
+}
+
+std::string SingleResamplePassEffect::output_fragment_shader()
+{
+ char buf[256];
+ sprintf(buf, "#define DIRECTION_VERTICAL %d\n", (direction == VERTICAL));
+ return buf + read_file("resample_effect.frag");
+}
+
+// Using vertical scaling as an example:
+//
+// Generally out[y] = w0 * in[yi] + w1 * in[yi + 1] + w2 * in[yi + 2] + ...
+//
+// Obviously, yi will depend on y (in a not-quite-linear way), but so will
+// the weights w0, w1, w2, etc.. The easiest way of doing this is to encode,
+// for each sample, the weight and the yi value, e.g. <yi, w0>, <yi + 1, w1>,
+// and so on. For each y, we encode these along the x-axis (since that is spare),
+// so out[0] will read from parameters <x,y> = <0,0>, <1,0>, <2,0> and so on.
+//
+// For horizontal scaling, we fill in the exact same texture;
+// the shader just interprets is differently.
+//
+// TODO: Support optimization of wrapping the sample texture.
+// TODO: Support optimization using free linear sampling, like in BlurEffect.
+void SingleResamplePassEffect::update_texture(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
+{
+ unsigned src_size, dst_size;
+ if (direction == SingleResamplePassEffect::HORIZONTAL) {
+ assert(input_height == output_height);
+ src_size = input_width;
+ dst_size = output_width;
+ } else if (direction == SingleResamplePassEffect::VERTICAL) {
+ assert(input_width == output_width);
+ src_size = input_height;
+ dst_size = output_height;
+ } else {
+ assert(false);
+ }
+
+ // Sample the kernel in the right place. A diagram with a triangular kernel
+ // (corresponding to linear filtering, and obviously with radius 1)
+ // for easier ASCII art drawing:
+ //
+ // *
+ // / \ |
+ // / \ |
+ // / \ |
+ // x---x---x x x---x---x---x
+ //
+ // Scaling up (in this case, 2x) means sampling more densely:
+ //
+ // *
+ // / \ |
+ // / \ |
+ // / \ |
+ // x-x-x-x-x-x x x x-x-x-x-x-x-x-x
+ //
+ // When scaling up, any destination pixel will only be influenced by a few
+ // (in this case, two) neighboring pixels, and more importantly, the number
+ // will not be influenced by the scaling factor. (Note, however, that the
+ // pixel centers have moved, due to OpenGL's center-pixel convention.)
+ // The only thing that changes is the weights themselves, as the sampling
+ // points are at different distances from the original pixels.
+ //
+ // Scaling down is a different story:
+ //
+ // *
+ // / \ |
+ // / \ |
+ // / \ |
+ // --x------ x --x-------x--
+ //
+ // Again, the pixel centers have moved in a maybe unintuitive fashion,
+ // although when you consider that there are multiple source pixels around,
+ // it's not so bad as at first look:
+ //
+ // * * * *
+ // / \ / \ / \ / \ |
+ // / X X X \ |
+ // / / \ / \ / \ \ |
+ // --x-------x-------x-------x--
+ //
+ // As you can see, the new pixels become averages of the two neighboring old
+ // ones (the situation for Lanczos is of course more complex).
+ //
+ // Anyhow, in this case we clearly need to look at more source pixels
+ // to compute the destination pixel, and how many depend on the scaling factor.
+ // Thus, the kernel width will vary with how much we scale.
+ float radius_scaling_factor = std::min(float(dst_size) / float(src_size), 1.0f);
+ int int_radius = lrintf(LANCZOS_RADIUS / radius_scaling_factor);
+ src_samples = int_radius * 2 + 1;
+ float *weights = new float[dst_size * src_samples * 2];
+ for (unsigned y = 0; y < dst_size; ++y) {
+ // Find the point around which we want to sample the source image,
+ // compensating for differing pixel centers as the scale changes.
+ float center_src_y = (y + 0.5f) * float(src_size) / float(dst_size) - 0.5f;
+ int base_src_y = lrintf(center_src_y);
+
+ // Now sample <int_radius> 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), LANCZOS_RADIUS);
+ weights[(y * src_samples + i) * 2 + 0] = weight * radius_scaling_factor;
+ weights[(y * src_samples + i) * 2 + 1] = (src_y + 0.5) / float(src_size);
+ }
+ }
+
+ // Encode as a two-component texture. Note the GL_REPEAT, which is not relevant
+ // right now, but will be later.
+ glActiveTexture(GL_TEXTURE0 + *sampler_num);
+ check_error();
+ glBindTexture(GL_TEXTURE_2D, texnum);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+ check_error();
+ glTexImage2D(GL_TEXTURE_2D, 0, GL_RG16F, src_samples, dst_size, 0, GL_RG, GL_FLOAT, weights);
+ check_error();
+
+ delete[] weights;
+
+}
+
+void SingleResamplePassEffect::set_gl_state(GLuint glsl_program_num, const std::string &prefix, unsigned *sampler_num)
+{
+ Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+ if (input_width != last_input_width ||
+ input_height != last_input_height ||
+ output_width != last_output_width ||
+ output_height != last_output_height) {
+ update_texture(glsl_program_num, prefix, sampler_num);
+ last_input_width = input_width;
+ last_input_height = input_height;
+ last_output_width = output_width;
+ last_output_height = output_height;
+ }
+
+ glActiveTexture(GL_TEXTURE0 + *sampler_num);
+ check_error();
+ glBindTexture(GL_TEXTURE_2D, texnum);
+ check_error();
+
+ set_uniform_int(glsl_program_num, prefix, "sample_tex", *sampler_num);
+ ++sampler_num;
+ set_uniform_int(glsl_program_num, prefix, "num_samples", src_samples);
+
+ // Instructions for how to convert integer sample numbers to positions in the weight texture.
+ set_uniform_float(glsl_program_num, prefix, "sample_x_scale", 1.0f / src_samples);
+ set_uniform_float(glsl_program_num, prefix, "sample_x_offset", 0.5f / src_samples);
+
+ // We specifically do not want mipmaps on the input texture;
+ // they break minification.
+ glActiveTexture(GL_TEXTURE0);
+ check_error();
+ glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+ check_error();
+}
projects / movit / blobdiff