CODEWITHSUNDEEP
c++matrixglslraycastingperspective
KiraHoneybee
KiraHoneybee

Reputation: 672

(GLSL) Orienting raycast object to camera space

I'm trying to orient a ray-cast shape to a direction in world space. Here's a picture of it working correctly:

correct

It works fine as long as the objects are pointing explicitly at the camera's focus point. But, if I pan the screen left or right, I get this:

Incorrect

So, the arrows are maintaining their orientation as if they were still looking at the center of the screen.

I know my problem here is that I'm not taking the projection matrix into account to tweak the direction the object is pointing. However, anything I try only makes things worse.

Here's how I'm drawing it: I set up these vertices:

float aUV=.5f;
Vertex aV[4];
aV[0].mPos=Vector(-theSize,-theSize,0);
aV[0].mUV=Point(-aUV,-aUV);
aV[1].mPos=Vector(theSize,-theSize,0);
aV[1].mUV=Point(aUV,-aUV);
aV[2].mPos=Vector(-theSize,theSize,0);
aV[2].mUV=Point(-aUV,aUV);
aV[3].mPos=Vector(theSize,theSize,0);
aV[3].mUV=Point(aUV,aUV);

// Position (in 3d space) and a point at direction are sent in as uniforms.
// The UV of the object spans from -.5 to .5 to put 0,0 at the center.

So the vertex shader just draws a billboard centered at a position I send (and using the vertex's position to determine the billboard size).

For the fragment shader, I do this:

vec3 aRayOrigin=vec3(0.,0.,5.);
vec3 aRayDirection=normalize(vec3(vertex.mUV,-2.5));
//
// Hit object located at 0,0,0 oriented to uniform_Pointat's direction
//
vec4 aHH=RayHitObject(aRayOrigin,aRayDirection,uniform_PointAt.xyz);
if (aHH.x>0.0) // Draw the fragment

I compute the final PointAt (in C++, outside of the shader), oriented to texture space, like so:

Matrix aMat=getWorldMatrix().Normalized();
aMat*=getViewMatrix().Normalized();
Vector aFinalPointAt=pointAt*aMat; // <- Pass this in as uniform

I can tell what's happening-- I'm shooting rays straight in no matter what, but when the object is near the edge of the screen, they should be getting tweaked to approach the object from the side. I've been trying to factor that into the pointAt, but whenever I add the projection matrix to that calculation, I get worse results.

How can I change this to make my arrows maintain their orientation even when perspective becomes an issue? Should I be changing the pointAt value, or should I be trying to tweak the ray's direction? And whichever is smarter-- what's the right way to do it?

Upvotes: 0

Views: 172

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