+// OpenGL uses a bottom-left coordinate system, .flo files use a top-left coordinate system.
+void flip_coordinate_system(float *dense_flow, unsigned width, unsigned height)
+{
+ for (unsigned i = 0; i < width * height; ++i) {
+ dense_flow[i * 2 + 1] = -dense_flow[i * 2 + 1];
+ }
+}
+
+void write_flow(const char *filename, const float *dense_flow, unsigned width, unsigned height)
+{
+ FILE *flowfp = fopen(filename, "wb");
+ fprintf(flowfp, "FEIH");
+ fwrite(&width, 4, 1, flowfp);
+ fwrite(&height, 4, 1, flowfp);
+ for (unsigned y = 0; y < height; ++y) {
+ int yy = height - y - 1;
+ fwrite(&dense_flow[yy * width * 2], width * 2 * sizeof(float), 1, flowfp);
+ }
+ fclose(flowfp);
+}
+
+void write_ppm(const char *filename, const float *dense_flow, unsigned width, unsigned height)
+{
+ FILE *fp = fopen(filename, "wb");
+ fprintf(fp, "P6\n%d %d\n255\n", width, height);
+ for (unsigned y = 0; y < unsigned(height); ++y) {
+ int yy = height - y - 1;
+ for (unsigned x = 0; x < unsigned(width); ++x) {
+ float du = dense_flow[(yy * width + x) * 2 + 0];
+ float dv = dense_flow[(yy * width + x) * 2 + 1];
+
+ uint8_t r, g, b;
+ flow2rgb(du, dv, &r, &g, &b);
+ putc(r, fp);
+ putc(g, fp);
+ putc(b, fp);
+ }
+ }
+ fclose(fp);
+}
+
+void finish_one_read(GLuint width, GLuint height)
+{
+ assert(!reads_in_progress.empty());
+ ReadInProgress read = reads_in_progress.front();
+ reads_in_progress.pop_front();
+
+ unique_ptr<float[]> flow(new float[width * height * 2]);
+ void *buf = glMapNamedBufferRange(read.pbo, 0, width * height * 2 * sizeof(float), GL_MAP_READ_BIT); // Blocks if the read isn't done yet.
+ memcpy(flow.get(), buf, width * height * 2 * sizeof(float));
+ glUnmapNamedBuffer(read.pbo);
+ spare_pbos.push(read.pbo);
+
+ flip_coordinate_system(flow.get(), width, height);
+ if (!read.flow_filename.empty()) {
+ write_flow(read.flow_filename.c_str(), flow.get(), width, height);
+ fprintf(stderr, "%s %s -> %s\n", read.filename0.c_str(), read.filename1.c_str(), read.flow_filename.c_str());
+ }
+ if (!read.ppm_filename.empty()) {
+ write_ppm(read.ppm_filename.c_str(), flow.get(), width, height);
+ }
+}
+
+void schedule_read(GLuint tex, GLuint width, GLuint height, const char *filename0, const char *filename1, const char *flow_filename, const char *ppm_filename)
+{
+ if (spare_pbos.empty()) {
+ finish_one_read(width, height);
+ }
+ assert(!spare_pbos.empty());
+ reads_in_progress.emplace_back(ReadInProgress{ spare_pbos.top(), filename0, filename1, flow_filename, ppm_filename });
+ glBindBuffer(GL_PIXEL_PACK_BUFFER, spare_pbos.top());
+ spare_pbos.pop();
+ glGetTextureImage(tex, 0, GL_RG, GL_FLOAT, width * height * 2 * sizeof(float), nullptr);
+ glBindBuffer(GL_PIXEL_PACK_BUFFER, 0);
+}
+