I think I broke C

[price3]

I am student doing the typical ray tracer in C on Sun Sparc. One of the features is glossy reflections, where the reflected angle is slightly skewed a number of times depending on a variable, and the resulting color is averaged. The problem is, all the glossy reflections come out pure white. You may think the color is not being averaged properly, but the strange part is, when a put a printf statement in the code to check the value of the color, it works. When the printf is commented out, the value is Not a Number (NaN), producing the white.... How can a printf statement cause this?


//check for reflections
if (hit.obj->specular.x > 0 || hit.obj->specular.y > 0 ||
hit.obj->specular.z > 0) {
int g,k;
g = scene->glossRays; //this value is 1.
Color newCol = {0,0,0}; // Color is 3 doubles for rgb

for (k = 0; k < g; k++) {
Ray rray; //ray is a vector and direction

if (hit.obj->glossy > 0.0) {
rray = reflectedRayG(ray, &normal, &hitPt, hit.obj->glossy);
} //glossy reflections call

else {
rray = reflectedRay(ray, &normal, &hitPt);
} //non glossy reflections

Color rc = shootRay(scene, &rray, bounce +1);
v3Print(&rc); // this is the printf to stderr that prints the color
// if commented out, newCol is NaN
// if left in, it works properly

newCol.x += hit.obj->specular.x * rc.x;
newCol.y += hit.obj->specular.y * rc.y;
newCol.z += hit.obj->specular.z * rc.z;
}// for k
v3Print(&newCol); //error checking color
newCol = v3Scale(&newCol, 1/(float)g);
c = v3Sum(&c, &newCol);
}//if reflections

[Banfa]

This sort of symptom is often indicative of a dangling pointer and that in turn means the the source of the problem is not necessarily in the piece of code where the error comes to light.

You will have to check you code for possible writes to invalid pointers.

[price3]

You were exactly right. The part of my light structure that contained the location was being stored as a pointer, not a vector, and was dropping off the stack. I would have found it sooner if it had actually crashed when reading NaN values in a vector instead of outputting the color white. Thanks so much!