Gradient algorithm produces little white dots - c++

Question

I'm working on an algorithm to generate point to point linear gradients. I have a rough proof of concept implementation done:
GLuint OGLENGINEFUNCTIONS::CreateGradient( std::vector<ARGBCOLORF> &input,POINTFLOAT start, POINTFLOAT end, int width, int height,bool radial )
{
std::vector<POINT> pol;
std::vector<GLubyte> pdata(width * height * 4);
std::vector<POINTFLOAT> linearpts;
std::vector<float> lookup;
float distance = GetDistance(start,end);
RoundNumber(distance);
POINTFLOAT temp;
float incr = 1 / (distance + 1);
for(int l = 0; l < 100; l ++)
{
POINTFLOAT outA;
POINTFLOAT OutB;
float dirlen;
float perplen;
POINTFLOAT dir;
POINTFLOAT ndir;
POINTFLOAT perp;
POINTFLOAT nperp;
POINTFLOAT perpoffset;
POINTFLOAT diroffset;
dir.x = end.x - start.x;
dir.y = end.y - start.y;
dirlen = sqrt((dir.x * dir.x) + (dir.y * dir.y));
ndir.x = static_cast<float>(dir.x * 1.0 / dirlen);
ndir.y = static_cast<float>(dir.y * 1.0 / dirlen);
perp.x = dir.y;
perp.y = -dir.x;
perplen = sqrt((perp.x * perp.x) + (perp.y * perp.y));
nperp.x = static_cast<float>(perp.x * 1.0 / perplen);
nperp.y = static_cast<float>(perp.y * 1.0 / perplen);
perpoffset.x = static_cast<float>(nperp.x * l * 0.5);
perpoffset.y = static_cast<float>(nperp.y * l * 0.5);
diroffset.x = static_cast<float>(ndir.x * 0 * 0.5);
diroffset.y = static_cast<float>(ndir.y * 0 * 0.5);
outA.x = end.x + perpoffset.x + diroffset.x;
outA.y = end.y + perpoffset.y + diroffset.y;
OutB.x = start.x + perpoffset.x - diroffset.x;
OutB.y = start.y + perpoffset.y - diroffset.y;
for (float i = 0; i < 1; i += incr)
{
temp = GetLinearBezier(i,outA,OutB);
RoundNumber(temp.x);
RoundNumber(temp.y);
linearpts.push_back(temp);
lookup.push_back(i);
}
for (unsigned int j = 0; j < linearpts.size(); j++) {
if(linearpts[j].x < width && linearpts[j].x >= 0 &&
linearpts[j].y < height && linearpts[j].y >=0)
{
pdata[linearpts[j].x * 4 * width + linearpts[j].y * 4 + 0] = (GLubyte) j;
pdata[linearpts[j].x * 4 * width + linearpts[j].y * 4 + 1] = (GLubyte) j;
pdata[linearpts[j].x * 4 * width + linearpts[j].y * 4 + 2] = (GLubyte) j;
pdata[linearpts[j].x * 4 * width + linearpts[j].y * 4 + 3] = (GLubyte) 255;
}
}
lookup.clear();
linearpts.clear();
}
return CreateTexture(pdata,width,height);
}
It works as I would expect most of the time, but at certain angles it produces little white dots. I can't figure out what does this.
This is what it looks like at most angles (good) http://img9.imageshack.us/img9/5922/goodgradient.png
But once in a while it looks like this (bad): http://img155.imageshack.us/img155/760/badgradient.png
What could be causing the white dots?
Is there maybe also a better way to generate my gradients if no solution is possible for this?
Thanks

Answer 1

I think you have a bug indexing into the pdata byte vector. Your x domain is [0, width) but when you multiply out the indices you're doing x * 4 * width. It should probably be x * 4 + y * 4 * width or x * 4 * height + y * 4 depending on whether you're data is arranged row or column major.