plastic

03-31-2016, 07:39 AM

I have been trying to implement a ray tracer in my fragment shader. And I need to clear off some confusions first:

i) I have scan through some example ray tracer, and I find that most of them tend to use the fragCoord to cast the ray. But I have been wondering why don't they use eye and vertex coordinate to cast the ray? Please correct me if I am wrong here, the camera/eye is at (0,0,0) in eye coordinate. And suppose we multiply vertex with modelview matrix: myvertex = (ModeviewMAtrix * vertex) , we get a result of vertex in eye coordinate stored in myvertex. Is it appropriate to cast a ray with ray.Origin at (0,0,0) and direction of the ray is the position of myvertex in normalized form?

I am trying to do a very basic stuff only here, drawing 2 sphere with different ambient different material, no lighting calculation involve yet, I just want my shader to be able to correctly map the correct ambient color onto my spheres

size 640 480 // window size

camera 0 -4 4 0 0 0 0 1 1 45 //eye, center, up, fovy

pushTransform // first sphere should look grey color

ambient .7 .7 .7

sphere 0 0 0 1 // xyz radius

popTransform;

pushTransform // 2nd sphere, purple

translate 2 0 0

ambient .1 .7 .7

sphere 0 0 0 1

popTransform;

//vertex shader

void main() {

gl_Position = pm * mv * vec4(vertices, 1.0) ; // pm and mv are uniforms for projection and modelview mat

myvertex = mv * vec4(vertices, 1.0) ; // vertices is the varying input passed from window with

}

//Fragment shader

//data for raytracer//

const int numObj = 2;

uniform vec4 ambData[numObj];

uniform vec4 diffData[numObj];

uniform vec4 specData[numObj];

uniform vec4 emiData[numObj];

uniform mat4 transfData[numObj];

uniform float shnData[numObj];

uniform int typeData[numObj];

uniform float sizeData[numObj];

uniform mat4 lookAt;

uniform int maxDepth;

//////////////////////

bool circleIntersect(in vec3 cen, in float r, in vec3 ori, in vec3 dir, inout float t ){

vec3 RC = ori - cen;

float DD = dot(dir, dir);

float DdRC = dot(dir, RC);

float sqtN, sqtP;

t = r*r - dot(RC,RC) + DdRC*DdRC;

if( t > 0.0 ) // 2 root

{

sqtP = sqrt(t) - DdRC;

sqtN = -sqtP - DdRC;

if (sqtP <= 0 && sqtN <= 0){

return false;

}

if (sqtN < sqtP){

t = sqtN;

}

else{

t = sqtP;

}

if (t <= 0)

return false;

return true;

}

return false;

}

vec4 intersection(in vec3 rayO, in vec3 rayD){

vec4 retClr = vec4(0.0);

float tMin = t_inf; //t_inf is a constant = 100 000.0f

float t = tMin;

vec3 norm;

int closestIdx;

for (int i = 0; i < numObj; i++){

if (typeData[i] == 2){

vec4 c = lookAt * transfData[i] * vec4(0.0, 0.0, 0.0, 1.0);

if (circleIntersect(c.xyz, 6.0, rayO, rayD, t)){

if (t < tMin){

closestIdx = i;

tMin = t;

}

}

else{

continue;

}

}

else if (typeData[i] == 4){

if (cubeIntersect(transfData[i], rayO, rayD, t, norm) ){

if (t < tMin){

closestIdx = i;

tMin = t;

}

}

else{

continue;

}

}

}

retClr = vec4(0,0,0,1) + ambData[closestIdx];

return retClr;

}

void main (void)

{

vec4 eye = vec4(0,0,0,1); //lookAt * vec4(0.0, -4.0, 4.0, 1.0);

vec3 rayOri = eye.xyz / eye.w;

vec3 rayDir = normalize(myvertex.xyz - eye.xyz);

gl_FragColor += intersection(rayOri, rayDir);

}

The result I get is 2 circle are drawn on the screen. But sadly both of them in purple color...I rotate the camera to see these 2 sphere from different directions but both of them look completely purple, no other color. I highly doubt my ray setup is totally wrong.

i) I have scan through some example ray tracer, and I find that most of them tend to use the fragCoord to cast the ray. But I have been wondering why don't they use eye and vertex coordinate to cast the ray? Please correct me if I am wrong here, the camera/eye is at (0,0,0) in eye coordinate. And suppose we multiply vertex with modelview matrix: myvertex = (ModeviewMAtrix * vertex) , we get a result of vertex in eye coordinate stored in myvertex. Is it appropriate to cast a ray with ray.Origin at (0,0,0) and direction of the ray is the position of myvertex in normalized form?

I am trying to do a very basic stuff only here, drawing 2 sphere with different ambient different material, no lighting calculation involve yet, I just want my shader to be able to correctly map the correct ambient color onto my spheres

size 640 480 // window size

camera 0 -4 4 0 0 0 0 1 1 45 //eye, center, up, fovy

pushTransform // first sphere should look grey color

ambient .7 .7 .7

sphere 0 0 0 1 // xyz radius

popTransform;

pushTransform // 2nd sphere, purple

translate 2 0 0

ambient .1 .7 .7

sphere 0 0 0 1

popTransform;

//vertex shader

void main() {

gl_Position = pm * mv * vec4(vertices, 1.0) ; // pm and mv are uniforms for projection and modelview mat

myvertex = mv * vec4(vertices, 1.0) ; // vertices is the varying input passed from window with

}

//Fragment shader

//data for raytracer//

const int numObj = 2;

uniform vec4 ambData[numObj];

uniform vec4 diffData[numObj];

uniform vec4 specData[numObj];

uniform vec4 emiData[numObj];

uniform mat4 transfData[numObj];

uniform float shnData[numObj];

uniform int typeData[numObj];

uniform float sizeData[numObj];

uniform mat4 lookAt;

uniform int maxDepth;

//////////////////////

bool circleIntersect(in vec3 cen, in float r, in vec3 ori, in vec3 dir, inout float t ){

vec3 RC = ori - cen;

float DD = dot(dir, dir);

float DdRC = dot(dir, RC);

float sqtN, sqtP;

t = r*r - dot(RC,RC) + DdRC*DdRC;

if( t > 0.0 ) // 2 root

{

sqtP = sqrt(t) - DdRC;

sqtN = -sqtP - DdRC;

if (sqtP <= 0 && sqtN <= 0){

return false;

}

if (sqtN < sqtP){

t = sqtN;

}

else{

t = sqtP;

}

if (t <= 0)

return false;

return true;

}

return false;

}

vec4 intersection(in vec3 rayO, in vec3 rayD){

vec4 retClr = vec4(0.0);

float tMin = t_inf; //t_inf is a constant = 100 000.0f

float t = tMin;

vec3 norm;

int closestIdx;

for (int i = 0; i < numObj; i++){

if (typeData[i] == 2){

vec4 c = lookAt * transfData[i] * vec4(0.0, 0.0, 0.0, 1.0);

if (circleIntersect(c.xyz, 6.0, rayO, rayD, t)){

if (t < tMin){

closestIdx = i;

tMin = t;

}

}

else{

continue;

}

}

else if (typeData[i] == 4){

if (cubeIntersect(transfData[i], rayO, rayD, t, norm) ){

if (t < tMin){

closestIdx = i;

tMin = t;

}

}

else{

continue;

}

}

}

retClr = vec4(0,0,0,1) + ambData[closestIdx];

return retClr;

}

void main (void)

{

vec4 eye = vec4(0,0,0,1); //lookAt * vec4(0.0, -4.0, 4.0, 1.0);

vec3 rayOri = eye.xyz / eye.w;

vec3 rayDir = normalize(myvertex.xyz - eye.xyz);

gl_FragColor += intersection(rayOri, rayDir);

}

The result I get is 2 circle are drawn on the screen. But sadly both of them in purple color...I rotate the camera to see these 2 sphere from different directions but both of them look completely purple, no other color. I highly doubt my ray setup is totally wrong.