/*
 compiling with:  ../../bin/diderotc --exec bug042.diderot
 produces error:

uncaught exception Fail [Fail: lookup(_, l__t_217)]
  raised at common/phase-timer.sml:78.50-78.52
  raised at common/phase-timer.sml:78.50-78.52
  raised at c-util/tree-to-c.sml:69.29-69.70

*/
// set camera, image, and rendering parameters
input vec3 camEye = [0.09, 0, 10];
input vec3 camAt = [0.09, 0, 0];
input vec3 camUp = [-1, 0, 0];
input real camNearAtRel = -0.45;
input real camFarAtRel =  0.45;
input real camFOV = 4.85;
input int iresU = 450;
input int iresV = 200;
input real refStep = 0.005;
input real rayStep = 0.005;
input vec3 lightVsp = [-2, -3, -4];
input real phongKa = 0.3;
input real phongKd = 0.7;
input real thickness = 0.017;

input real isoval = -0.1;

field#2(3)[] F = c4hexic ⊛ image("../data/wee-torus.nrrd");

function real alpha(real v, real g) = max(0, 1 - |v/g|/thickness);

// (boilerplate) computation of camera and light info
real camDist = |camAt - camEye|;
real camNear = camNearAtRel + camDist;
real camFar = camFarAtRel + camDist;
vec3 camN = normalize(camAt - camEye);  // away
vec3 camU = normalize(camN × camUp);    // right
vec3 camV = camU × camN;                // up
real camVmax = tan(camFOV*π/360)*camDist;
real camUmax = camVmax*iresU/iresV;
vec3 light = transpose([camU,camV,camN])•normalize(lightVsp);

strand raycast(int ui, int vi) {
  real rayU = lerp(-camUmax, camUmax, -0.5, ui, iresU-0.5);
  real rayV = lerp(camVmax, -camVmax, -0.5, vi, iresV-0.5);
  real rayN = camNear;
  vec3 rayVec = camN + (rayU*camU + rayV*camV)/camDist;
  real transp = 1;
  vec3 rgb = [0,0,0];
  output vec4 rgba = [0,0,0,0];

  update {
    vec3 x = camEye + rayN*rayVec;
    if (inside(x,F)) {
      vec3 grad = -∇F(x);
      real a = 0;
      real val = F(x) - isoval;
      a = alpha(val, |grad|);
      if (a > 0) {  // we have some opacity
        a = 1 - pow(1-a, rayStep*|rayVec|/refStep);
        real depth = lerp(1.3, 0.6, camNear, rayN, camFar);
        real shade = max(0, normalize(grad)•light);
        rgb += transp*depth*a*(phongKa + phongKd*shade)*[1,1,1];
        transp *= 1 - a;
      }
    }
    if (transp < 0.01) {  // early ray termination
      transp = 0;
      stabilize;
    }
    if (rayN > camFar) {
      stabilize;
    }
    rayN = rayN + rayStep;
  }
  stabilize {
    real a = 1-transp;
    if (a > 0) rgba = [rgb[0]/a, rgb[1]/a, rgb[2]/a, a];
  }
}
initially [ raycast(ui, vi) | vi in 0..iresV-1, ui in 0..iresU-1 ];

<script type="text/javascript">//<![CDATA[
		function toggle_ffErrors() {
			var errorsblock = document.getElementById("ffErrorsBlock");
			var errorsgroup = document.getElementById("ffErrors");
			if (errorsblock.style.display == "none") {
				errorsblock.style.display = "block";
				errorsgroup.style.right = "10px";
			} else {
				errorsblock.style.display = "none";
				errorsgroup.style.right = "300px";
			}
		}
//]]></script>
<div id="ffErrors">
<a href="javascript:toggle_ffErrors();">Click to toggle</a>
<div id="ffErrorsBlock">
	<div class="error">does not end with &lt;/html&gt; tag</div>
	<div class="error">does not end with &lt;/body&gt; tag</div>
	<div class="info">The output has ended thus: a, rgb[1]/a, rgb[2]/a, a];
  }
}
initially [ raycast(ui, vi) | vi in 0..iresV-1, ui in 0..iresU-1 ];</div>
</div></div>
</body></html>