Feat/raycast skeleton - #227
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This is to allow to avoid intersecting points at the ends of the lines
Old calls just pass gl fragcoord.z as this depth
These are screen space camera facing quads where geometry hit/miss, depth, and lighting contribution are determined via raycast (and generally intended to be an analytic raycast for speed not a raymarch)
The old cylinder used an OBB but the new one doesn't and AABB is faster and simpler
This is formed by: 1. Find AABB of the sphere. Project the 8 corners of the AABB into screen space and then draw 6 verts (two tris) to represent the quad in screen space which covers the AABB as the vertex shader. For now each invocation redoes the projection, which could possibly be avoided but seems a small win. Rest happens in frag shader. 2. Find the ray from the eye (camera) to the fragment, in model space. 3. With this ray, see if a part of the ray forms a chord through the sphere. To do this, get the shortest distance from the ray to the sphere center (which is the perpendicular) and see if the right angled triangle that would be formed between a radial line from the sphere center and the perpendicular could exist. 4. If the above holds, so there is a chord, ensure that the ray doesn't need to travel backwards behind the near plane to form the chord (which would be negative hit distance) 5. If no hit, discard. If hit, continue with regular depth and lighting calculation based on the hit distance.
the analogy here is similar to when a camera in a game goes behind a wall, often you then don't render the wall because you're inside the wall. We'd have the same issue of the camera getting trapped inside a sphere if the sphere was big enough.
Follows a very similar process to the AABB, where we provide the parameterization of the OBB to the vertex shader, and construct the projection to clip space of the model space OBB to find a screen space quad which covers the screen space (depth clipped) OBB. However the calculations are a bit more complex since we have a OBB instead of an AABB.
Adds a raycast cylinder building on the OBB form in the generic file. The vertex shader setup is quite small with the generic helper. For the fragment shader we split the problem into two parts. We start by considering the line that represents the primary axis going through the center of the cylinder, which we have from its two endpoints. Then for this axis line, we find the plane perpendicular to the axis line. We check in that plane in a very similar manner to whether in our sphere code the radial line and the perpendicular could form a right angled triangle or not to see if we have a hit with the cylinder in the plane. If we do, then we just need to check if the hit lies outside the ends of the cylinder when viewed along the main axis running through the center of the cylinder. If it is within a sufficient distance, we can consider the ray to be a hit. To split into the axial component and the planar component we use the dot product. The hit point is fairly simple from there in the plane, and for the normal, since we constructed the plane to be perpendicular to the axis line, we can use the information about the orientation of the plane to determine the normal as the normal will be in the same direction as the in-plane radial line starting from the cylinder central axis line.
Should but perf improvements, which is helpful with the cylinder rendering
Also combines the rendering tests together
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Sphere:
Cylinder:
