tri.cpp

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#include <cv.h>

static const bool no_clipping=false;

static int edge_pair(IplImage *im, int sum[], int _a[2], int _b[2], int _c[2], int _d[2])
{
        int a[2];
        int b[2];
        int c[2];
        int d[2];

        if (_a[1] > _b[1]) {
                b[0] = _a[0];
                b[1] = _a[1];
                a[0] = _b[0];
                a[1] = _b[1];
        } else {
                a[0] = _a[0];
                a[1] = _a[1];
                b[0] = _b[0];
                b[1] = _b[1];
        }

        if (_c[1] > _d[1]) {
                d[0] = _c[0];
                d[1] = _c[1];
                c[0] = _d[0];
                c[1] = _d[1];
        } else {
                c[0] = _c[0];
                c[1] = _c[1];
                d[0] = _d[0];
                d[1] = _d[1];
        }

        int y_start = MAX(a[1], c[1]);
        int y_stop = MIN(b[1], d[1]);

        if (y_start >= y_stop) return 0;

        if (y_start < 0) {
                if (no_clipping) return 0;
                y_start = 0;
        }
        if (y_stop >= im->height) {
                if (no_clipping) return 0;
                y_stop = im->height - 1;
        }
        
        float slope1 = float(b[0] - a[0])/float(b[1]-a[1]);
        float delta1 = a[0] - slope1*a[1];

        float slope2 = float(d[0] - c[0])/float(d[1]-c[1]);
        float delta2 = c[0] - slope2*c[1];

        int x_step = im->nChannels;
        assert (im->depth == IPL_DEPTH_8U);

        int r=0;

        for (int y = y_start; y<y_stop; ++y) {

                float fy = (float) y;
                float x1 = slope1 * fy + delta1;
                float x2 = slope2 * fy + delta2;
                float minx = (x1 < x2 ? x1 : x2);
                int maxx = (int)(x1 > x2 ? x1 : x2);
                if (maxx < 0) continue;
                int x_start = (int)minx;
                if (x_start > im->width) {
                        if (no_clipping) return 0;
                        continue;
                }
                if (x_start < 0) {
                        if (no_clipping) return 0;
                        x_start = 0;
                }

                if (maxx >= im->width) maxx=im->width-1;
                int len = maxx-x_start;
                if (len >0) {
                        r += len;
                        unsigned char *ptr = (unsigned char *)im->imageData + y*im->widthStep + x_start*x_step;

                        if (im->nChannels>1) 
                                for (int x=0; x<len; ++x) {
                                        for (int c=0;c<im->nChannels;++c) {
                                                sum[c] += *ptr++;
                                        }
                                } 
                        else
                                for (int x=0; x<len; ++x)
                                        sum[0] += *ptr++;
                }
        }
        return r;
}

int stat_triangle(IplImage *im, int pts[3][2], float avg[3]) 
{
        int sum[3] = {0,0,0};
        // for every edge pair...
        int a = edge_pair(im, sum, pts[0], pts[1], pts[0], pts[2]);
        int b = edge_pair(im, sum, pts[0], pts[1], pts[1], pts[2]);
        int c = edge_pair(im, sum, pts[1], pts[2], pts[0], pts[2]);
        int tot = a+b+c;
        if (no_clipping) {
                if (a==0 || b==0 || c==0) tot=0;
        }
        if (tot>0) {
                float ftot = (float)tot;
                avg[0] = float(sum[0])/ftot;
                avg[1] = float(sum[1])/ftot;
                avg[2] = float(sum[2])/ftot;
        } else {
                avg[0] = avg[1] = avg[2] = -1;
        }
        if (im->nChannels==1) {
                avg[1] = avg[2] = -1;
        }
        return tot;
}