Bicubic Interpolation for Image Resizing

uint Interpolate_Value(uint v0, uint v1, uint v2, uint v3, float t)
{
	int p = (v3 - v2) - (v0 - v1);
	int q = (v0 - v1) - p;
	int r = v2 - v0;
	int s = v1;
	float tSqrd = t * t;
//
	return (p * (tSqrd * t)) + (q * tSqrd) + (r * t) + s;
	//return (p * (tSqrd * t) + 0.5f) + (q * tSqrd + 0.5f) + (r * t + 0.5f) + s; // Use this one for nicer interpolation, it rounds instead of truncates.
}
//
// To interpolate a pixel we need to interpolate each color component seperately
//
ARGB Interpolate_Pixel(ARGB p0, ARGB p1, ARGB p2, ARGB p3, float t)
{
	return InterpolateValue(p0.a, p1.a, p2.a, p3.a, t) << 24 |
	       InterpolateValue(p0.r, p1.r, p2.r, p3.r, t) << 16 |
	       InterpolateValue(p0.g, p1.g, p2.g, p3.g, t) << 08 |
	       InterpolateValue(p0.b, p1.b, p2.b, p3.b, t);
}
//
//
//
Resize_Image(ARGB *Image, uint Width, uint Height, uint NewWidth, uint NewWidth, ARGB *NewImage)
{
	uint	OldImageX, OldImageY;
	float	dx = Width / NewWidth, dy = Height / NewHeight;
	ARGB	Temp[4];
//	
//
	for (y = 0; y < NewHeight; ++y)
	{
		OldImageY = dy * y;
		ty = dy * y - OldImageY;
//
		for (x = 0; x < NewWidth; ++x)
		{
			OldImageX = dx * x;
			tx = dx * x - OldImageX;
//
			// I don't know how image scaling works with regards to edges
			// e.g. when OldImageX is 0 and you need pixels from behind (OldImageX - 1) you can either wrap around and get pixels to sample from the other side of the image (OldImageX = Width - 1)
			// or you can just clamp to the edge (if (OldImageX - 1 < 0) OldImageX = 0), your choice, see what looks best.
			// Likewise for when OldImageX == Width - 1 and you need to get OldImageX + 1
//
			// To interpolate 2D data correctly we first interpolate 4 pixels horizontally for each of 4 scanlines, which leaves us with 4 new pixels
//
			Temp[0] = Interpolate_Pixel(Image[(OldImageY - 1) * Width + OldImageX - 1],
						Image[(OldImageY - 1) * Width + OldImageX],
						Image[(OldImageY - 1) * Width + OldImageX + 1],
						Image[(OldImageY - 1) * Width + OldImageX + 2],
						tx);
			Temp[1] = Interpolate_Pixel(Image[OldImageY * Width + OldImageX - 1],
						Image[OldImageY * Width + OldImageX],
						Image[OldImageY * Width + OldImageX + 1],
						Image[OldImageY * Width + OldImageX + 2],
						tx);
			Temp[2] = Interpolate_Pixel(Image[(OldImageY + 1) * Width + OldImageX - 1],
						Image[(OldImageY + 1) * Width + OldImageX],
						Image[(OldImageY + 1) * Width + OldImageX + 1],
						Image[(OldImageY + 1) * Width + OldImageX + 2],
						tx);
			Temp[3] = Interpolate_Pixel(Image[(OldImageY + 2) * Width + OldImageX - 1],
						Image[(OldImageY + 2) * Width + OldImageX],
						Image[(OldImageY + 2) * Width + OldImageX + 1],
						Image[(OldImageY + 2) * Width + OldImageX + 2],
						tx);
//
			// Then we interpolate those 4 pixels to get a single pixel that is a composite of 4 * 4 pixels, 16 pixels
			NewImage[y * NewWidth + x] = Interpolate_Pixel(Temp[0], Temp[1], Temp[2], Temp[3], ty);
		}
	}
}