Ray tracing algorithm as a stack?

/*
	Unrolled recursive function.
	
	At each level in the tree we must evaluate the reflection ray and the transmission ray.
	
	When the intersection is calculated, both tRay and rRay are calculated along with kr and kt.
	
	To ensure that intersection is called minimally we must therefore have at least 4 stacks. 
	The tRay, the rRay, kt and kr.
	
	We also need a state that tells us which ray we have processed (ray, t or r). This must also be stacked so
	that makes 5 stacks. 
*/
 
// Two stages at each level.
Ray tStack[MAX];
Ray rStack[MAX];
int ktStack[MAX];
int krStack[MAX];
// Next ray to process at this level (tRay or rRay).
#define STATE_T_RAY (0)
#define STATE_R_RAY (1)
#define STATE_COMPLETE (2)
int trStack[MAX];
int d; // Depth.
 
color traceRay(ray) {
	// Start at depth 0.
	d = 0;
	// Keep walking the tree until we get back to depth 0.
	do {
		// Trace the ray.
		if ( intersection(ray) ) {
			// Keep the results of the intersection call at the current level.
			tStack[d] = trans_ray;
			ktStack[d] = kt;
			rStack[d] = reflect_ray;
			krStack[d] = kr;
			// Next state at this level is to check the t ray.
			trStack[d] = STATE_T_RAY;
		} else {
			// No intersection, add background colour
			retcolor += background_color;
			//  and were done at this level.
			d -= 1;
		}
		
		// Which ray should we work on for the next iteration?
 
		// Initially nothing.
		ray = null;
		// Walk the stack till we're done or we know which ray to do next.
		while ( ray == null && d >= 0 ) {
			// Check the state.
			switch ( trStack[d] ) {
				case STATE_T_RAY:
					// Was there one?
					if ( d < MAX && ktStack[d] > 0 ) {
						// Do the transmission ray.
						ray = tStack[d];
						// Step my state.
						trStack[d] += 1;
						// Step up.
						trStack[++d] = STATE_T_RAY;
					}
					break;
					
				case STATE_R_RAY:
					// Was there one?
					if ( d < MAX && krStack[d] > 0 ) {
						// Do the reflection ray.
						ray = rStack[d];
						// Step my state.
						trStack[d] += 1;
						// Step up.
						trStack[++d] = STATE_T_RAY;
					}
					break;
					
				default:
					// Complete at this level, step out.
					d -= 1;
					break;
			}
		}
	} while( d >= 0 );
	
	return retcolor;
}	

/*
	Unrolled recursive function.
	
	At each level in the tree we must evaluate the reflection ray and the transmission ray.
	
	When the intersection is calculated, both tRay and rRay are calculated along with kr and kt.
	
	To ensure that intersection is called minimally we must therefore have at least 4 stacks. 
	The tRay, the rRay, kt and kr.
	
	We also need a state that tells us which ray we have processed (ray, t or r). This must also be stacked so
	that makes 5 stacks. 
*/
 
// Two stages at each level.
Ray tStack[MAX];
Ray rStack[MAX];
int ktStack[MAX];
int krStack[MAX];
// Next ray to process at this level (tRay or rRay).
#define STATE_T_RAY (0)
#define STATE_R_RAY (1)
#define STATE_COMPLETE (2)
int trStack[MAX];
int d; // Depth.
 
color traceRay(ray) {
	// Start at depth 0.
	d = 0;
	// Keep walking the tree until we get back to depth 0.
	do {
		// Trace the ray.
		if ( intersection(ray) ) {
			// Keep the results of the intersection call at the current level.
			tStack[d] = trans_ray;
			ktStack[d] = kt;
			rStack[d] = reflect_ray;
			krStack[d] = kr;
			// Next state at this level is to check the t ray.
			trStack[d] = STATE_T_RAY;
		} else {
			// No intersection, add background colour
			retcolor += background_color;
			//  and were done at this level.
			d -= 1;
		}
		
		// Which ray should we work on for the next iteration?
 
		// Initially nothing.
		ray = null;
		// Walk the stack till we're done or we know which ray to do next.
		while ( ray == null && d >= 0 ) {
			// Check the state.
			switch ( trStack[d] ) {
				case STATE_T_RAY:
					// Step my state.
					trStack[d] += 1;
					// Was there one?
					if ( ktStack[d] > 0 && d < MAX ) {
						// Do the transmission ray.
						ray = tStack[d];
						// Step up.
						trStack[++d] = STATE_T_RAY;
					}
					break;
					
				case STATE_R_RAY:
					// Step my state.
					trStack[d] += 1;
					// Was there one?
					if ( krStack[d] > 0 && d < MAX  ) {
						// Do the reflection ray.
						ray = rStack[d];
						// Step up.
						trStack[++d] = STATE_T_RAY;
					}
					break;
					
				default:
					// Complete at this level, step out.
					d -= 1;
					break;
			}
		}
	} while( d >= 0 );
	
	return retcolor;
}