Hi, I’m trying to implement the Soft Shadows in my macOS Objective-C application. Your sample playground looks gorgeous, but I cannot well understand how to achieve the same effect using a typical geometry passed to the Vertex Shader by drawIndexedPrimitives:.
How should I intercept the ray with the geometry?
And how should I dispatch the threads?
Is a sample code I can learn from?
I would advise exploring acceleration structures. Metal by Tutorials provides an introduction to ray tracing concepts, but doesn’t go so far.
Apple’s recent Metal 3 advances ray tracing on the GPU substantially.
Specifically, start off with the ray tracing WWDC videos from 2021 and 2022. There’s a ton of sample code too, most of it in Objective C.
The sample Accelerating ray tracing and motion blur produces shadows using an obj file.
Intel gave us a gift: Path tracing workshop
The first part of this shows how to do Ray-mesh intersection to see if rays hit triangles (rather than spheres and rectangles as described in MbT).
You should still explore Apple’s ray-tracing APIs though, as they will be optimised.
Thank you Caroline! This sounds really well. I have already taken a look at the Apple Hybrid Rendering. I will take this workshop and come back here soon. I am very interested in real time ray-tracing, path-tracing and rendering.
Hi Caroline,
I’m studying the Apple sample code about Path Tracing. That looks really cool. The code is here
I added a sphere to the scene, a texture to the objects, then I added the specular color effect to the shader. My camera is now movable/zoomable using the trackpad.
The Path Tracing is not in real time. It takes 2 or 3 seconds before the image looks well and loses the pixelated effect. And it’s a very simple scene with a few triangles. I can’t use it in an animation at 60 FPS nor 30 FPS while on the web everybody speaks about the real time path tracing as the latest revolution. Should I use a special video-card to achieve a good speed? Actually I’m working on a MacBook Pro 17" late 2019 (Intel) with an AMD Radeon Pro 5500M 4 GB. Is my video-card too slow or am I missing something in the code?
The final colours look pale (desaturated) even if I eliminate the tone mapping line of code from the copyFragment shader
// color = color / (1.0f + color);
Also I can’t understand why in the code the
uniforms->light.color is a vector3(4.0f, 4.0f, 4.0f). Why 4.0 and not 1.0 ?
float3 specularColor = 0;
if(bounce == 0)
{
if(diffuseFactor > 0.01)
{
float shininess = 200.0;
float attenuation = 1.0;
float specularIntensity = 1.0;
float3 V = ray.direction;
float3 R = normalize(reflect(lightDirection, surfaceNormal));
float specularFactor = pow(max(dot(V, R), 0.0), max(shininess, 1.0));
float specularSmooth = smoothstep(1e-3f, 1.0, specularFactor);
specularColor = uniforms.light.color * specularSmooth * attenuation * specularIntensity;
}
}
shadowRay.color = lightColor * color + specularColor;
The soft shadows are nice but their focus looks fixed. Instead usually the shadow looks well focused when the distance object-shadow is closer than the distance object-light.
The white spot you can see on the front wall looks “oval” and not “squared” as the light shape. It comes from the specular effect. It looks wrong.
I can’t yet find the way to add the mirror effect to the objects. Since the surfaces already partially get the colours from the walls aside (left and right) I thought it should be easy to reflect those walls (and any other objects on the scene) at 100%. I guess I misunderstood some concept.
As I have seen, the path tracing requires that I load the whole scene (vertex + normals, colours…) to the GPU using the accelerated structure and an intersector. Well. I can’t imagine yet how to rethink my structure of data since I have to pass to the GPU the materials, lights, textures, matrices (to animate the objects and the textures). I thought to use an object ID (to retrieve its mesh ID then its material) but I can’t think to add an object ID to any vertex of the scene. Is a well canonical way to structure the scene-data of my real time animation that well suite the path-tracing scheme?
P.S. Actually I have found a fine video-lesson about PathTracing. I write its link here for your convenience.
Hmm I don’t know that I can address these in a reasonable amount of time.
I don’t know enough about the most recent advances, but path tracing is enormously complicated, and requires a ton of hardware. NVIDIA has made the most advances in this field, and Apple is either playing catch-up, or coming up with their own hardware solution. (See point 7 re hybrid rendering)
It might be to do with your texture being sRGB and not matching the shader? The Apple sample looks fully saturated if I change their color values to being fully red/green.
x4 produces more light than x1. Try changing the values to 1.0 and see what you get.
For example, this hybrid rendering pipeline from Ray Tracing Gems:
Also see Apple’s talk on Hybrid Rendering: Explore hybrid rendering with Metal ray tracing - WWDC21 - Videos - Apple Developer
Thank you for the link. It looks like a great playlist: https://youtube.com/playlist?list=PLmIqTlJ6KsE2yXzeq02hqCDpOdtj6n6A9
If you want ray tracing shadows real time you will have to use the MPS denoiser on hybrid rendering.
this example shows exactly that.
