在OpenCV中的白色图像上画一条线

Question

I'm attempting to draw a graph on a blank image, using the cvLine method to go from point to point. Holder[] is an array of floaters. I have checked the array by printing out values, so it is not empty.

IplImage* blank = cvCreateImage(cvSize(640,480),IPL_DEPTH_8U,3); 
cvSet(blank, CV_RGB(255,255,255));

int i;
for (i = 0; i < height; i++) 
 {
cvLine(blank, cvPoint (i, holder[i]/100),  cvPoint (i+1, holder[i+1]/100), cvScalar(0,255,0),  8, 1);
 }

cvNamedWindow("Graph Title", 1);
cvShowImage("Graph Title", blank);
cvWaitKey(0);

When I run this code all I get is a white image, no plot.

Answer 1

I was able to fix it by declaring i and holder[i] inside the for loop, before the cvLine method.

for (i = 0; i < height; i++) 
{
int x1 = i;
int y1 = holder[i]/100;
int x2 = i + 1;
int y2 = holder[i+1]; 
cvLine(blank, cvPoint (x1, y1),  cvPoint (x2, y2), cvScalar(0,255,0),  8, 1);
}