Make flow writing a bit faster.

diff --git a/flow.cpp b/flow.cpp
index 001b14af8cd173068c36f4198211f4fc3dc648a5..93ac447f0021f7dacec0bbd2c9265ee0e6a2c561 100644 (file)
--- a/flow.cpp
+++ b/flow.cpp
@@ -1269,6 +1269,14 @@ void DISComputeFlow::release_texture(GLuint tex_num)
        assert(false);
 }
 
+// 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");
@@ -1277,15 +1285,7 @@ void write_flow(const char *filename, const float *dense_flow, unsigned width, u
        fwrite(&height, 4, 1, flowfp);
        for (unsigned y = 0; y < 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];
-
-                       dv = -dv;
-
-                       fwrite(&du, 4, 1, flowfp);
-                       fwrite(&dv, 4, 1, flowfp);
-               }
+               fwrite(&dense_flow[yy * width * 2], width * 2 * sizeof(float), 1, flowfp);
        }
        fclose(flowfp);
 }
@@ -1300,8 +1300,6 @@ void write_ppm(const char *filename, const float *dense_flow, unsigned width, un
                        float du = dense_flow[(yy * width + x) * 2 + 0];
                        float dv = dense_flow[(yy * width + x) * 2 + 1];
 
-                       dv = -dv;
-
                        uint8_t r, g, b;
                        flow2rgb(du, dv, &r, &g, &b);
                        putc(r, fp);
@@ -1404,6 +1402,7 @@ int main(int argc, char **argv)
 
        compute_flow.release_texture(final_tex);
 
+       flip_coordinate_system(dense_flow.get(), width1, height1);
        write_flow(flow_filename, dense_flow.get(), width1, height1);
        write_ppm("flow.ppm", dense_flow.get(), width1, height1);
 
@@ -1440,6 +1439,7 @@ int main(int argc, char **argv)
 
                compute_flow.release_texture(final_tex);
 
+               flip_coordinate_system(dense_flow.get(), width, height);
                write_flow(flow_filename, dense_flow.get(), width, height);
        }