Hybrid volume rendering in computer implemented animation
In the field of computer graphics and more specifically computer implemented animation, two known alternative methods for rendering objects which have volume (fire, smoke, clouds, etc.) are ray marching and splatting (i.e. particle-based rendering). These methods have contrasting strengths and weaknesses. The present volume rendering method and associated apparatus combine these methods, drawing on the strengths of each. The ray marches a volume but, rather than merely accumulating the samples along the ray, a distinct particle is generated for each sample. Each particle captures the volume's local attributes. The particles are then rendered through splatting. Thus the method has the strengths of splatting e.g., fast 3D motion blur and hardware rendering, and the strengths of ray marching e.g., volume sampling density corresponds with camera proximity since rays disperse, thereby focusing computer processing time on important volume detail and minimizing noise. The present method is useful in production of animated feature films, providing fast high-quality volume rendering with true 3D motion blur.
1 . A computer implemented method for depicting a volumetric effect occupying a volume, comprising the acts of:
providing a plurality of picture elements to define an image of the volumetric effect;
for each picture element casting a ray from an observation location through each picture element;
moving through the volume along each ray in increments;
at each increment, generating a particle;
rendering the particles; and
splatting each particle multiple times to define the image of the volumetric effect.
2 . The method of claim 1 , wherein the act of generating a particle includes interpolating.
3 . The method of claim 2 , wherein the interpolating is non-linear.
4 . The method of claim 2 wherein the interpolating includes applying one of a tri-linear, tri-quadratic, and tri-cubic interpolation.
5 . The method of claim 1 , wherein the rendering of the particles is individually or in batches.
6 . The method of claim 1 , wherein each particle is rendered on a quadrilateral the size of one of the picture elements.
7 . The method of claim 1 , wherein each particle has the attributes of position, color, opacity, and velocity.
8 . The method of claim 1 , wherein the observation location is that of a notional camera recording the image.
9 . The method of claim 1 , wherein the act of casting the ray includes for each ray:
determining its entry and exit point for the volume; and
applying an inverse transformation to the ray.
10 . The method of claim 1 , wherein the number of increments for each ray is in the range of 50 to 450.
11 . The method of claim 1 , wherein the act of splatting includes:
weighting each particle by a proportion of the associated pixel covered by the splatted particle.
12 . The method of claim 1 , wherein the act of splatting includes projecting a vector representing the velocity onto a plane defined by the picture elements, thereby to render motion blur.
13 . A computer readable medium storing computer code for carrying out the method of claim 1 .
14 . The method of claim 1 , further comprising repeating the act of splatting to provide motion blur.
15 . The method of claim 1 , further comprising setting a depth of field of the image.
16 . Computer implemented apparatus for depicting a volumetric effect occupying a volume, comprising:
a memory storing a plurality of picture elements defining an image;
a ray caster element coupled to the memory and casting a ray for each picture element from an observation location through each picture element;
a ray marcher element coupled to the ray caster and which moves through the volume along each ray in increments;
a particle generator element coupled to the ray marcher and which generates a particle at each increment;
a particle renderer element coupled to the particle generator and which renders the particles; and
a splatterer element coupled to the particle renderer element and which splats each particle multiple times to define the image of the volumetric effect.