Re: More fun with Kernel language.

• Subject: Re: More fun with Kernel language.
• From: Steve Israelson <email@hidden>
• Date: Tue, 27 Sep 2005 07:45:42 -0700
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Here is what I use to draw a line:  (my math sucks too:) )

I am basically doing what you are doing :)
Though I am making a full paint program....

/*
Draws a rounded line from p1 - p2 of thickness, size
*/

kernel vec4 drawLine(vec2 p1, vec2 p2, float size, __color inColor)
{
vec2 p3 = destCoord();

float u, d0,d1,d2, w = 1.0/size;
u = (p3.x - p1.x) * (p2.x - p1.x) + (p3.y - p1.y) * (p2.y - p1.y);
float dist;
dist = distance(p1, p2);
u = u / (dist*dist);

vec2  r;
r = p1 + u*(p2 - p1);
d0 = distance(r, p3);
d0 = 1.0 - clamp(d0 * w, 0.0, 1.0);

d0 = u < 0.0  ?  0.0  :  d0;
d0 = u > 1.0  ?  0.0  :  d0;

d1 = 1.0 - clamp(distance(p1, p3) * w, 0.0, 1.0);
d2 = 1.0 - clamp(distance(p2, p3) * w, 0.0, 1.0);

d0 = max(d0, max(d1,d2));
d0 = 1.0 - step(d0, 0.0); // 1.0 = inside, 0 = outside

vec4 color;
color.r = d0 * inColor.r;
color.g = d0 * inColor.g;
color.b = d0 * inColor.b;
color.a = d0 * inColor.a;
return color;
}

On 26-Sep-05, at 5:49 PM, John C. Randolph wrote:

Everyone,

As another step on my road to generating regular polygons in a CoreImage kernel, I hunted up some code on the net to compute the distance from a point to a line, and I now have the following kernel:

kernel vec4 drawLine(sampler image, float thickness, float Ax, float Ay, float Bx, float By)
I'm finding that my math skills were far rustier than I realized, so if anyone would care to take a pass at optimizing this code, I'm all ears. ;-) Also, I'd like to anti-alias the result. If anyone could offer a suggestion of how to do so, I'd certainly appreciate it.

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