shaderexp: add initial shader explorer tool (#245)

* shaderexp: first commit
* shaderexp: further improve error handling
* shaderexp: attribute ray_marching example

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
Co-authored-by: Stephen Gutekanst <stephen@hexops.com>

shaderexp/example-shaders/ray_marching.wgsl

@@ -0,0 +1,98 @@
+// A slight modification / translation of https://www.shadertoy.com/view/XlGBW3
+// to WGSL.
+// License: Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
+
+struct UniformBufferObject {
+    resolution: vec2<f32>,
+    time: f32,
+}
+@group(0) @binding(0) var<uniform> ubo : UniformBufferObject;
+
+fn getDist(p:vec3<f32>) -> f32{
+    let dist_from_center:f32 = 2.*sin(ubo.time * 3.);
+    let rotation_speed:f32 = 6.;
+    
+    let sphere1 = vec4<f32>(dist_from_center*cos(rotation_speed*ubo.time + 3.14159 * 0. * 2. / 3.),1.1, dist_from_center*sin(rotation_speed*ubo.time + 3.14159 + 3.14159 * 0. * 2. / 3.),1.);
+    let sphere2 = vec4<f32>(dist_from_center*cos(rotation_speed*ubo.time + 3.14159 * 1. * 2. / 3.),1.1, dist_from_center*sin(rotation_speed*ubo.time + 3.14159 + 3.14159 * 1. * 2. / 3.),1.);
+    let sphere3 = vec4<f32>(dist_from_center*cos(rotation_speed*ubo.time + 3.14159 * 2. * 2. / 3.),1.1, dist_from_center*sin(rotation_speed*ubo.time + 3.14159 + 3.14159 * 2. * 2. / 3.),1.);
+
+    let sphere1_dist:f32 = length(p - sphere1.xyz) - sphere1.w;
+    let sphere2_dist:f32 = length(p - sphere2.xyz) - sphere2.w;
+    let sphere3_dist:f32 = length(p - sphere3.xyz) - sphere3.w;
+    let plane_dist = p.y;
+    
+    return min(min(min(sphere1_dist,sphere2_dist),sphere3_dist),plane_dist);
+}
+
+fn rayMarch(ro:vec3<f32>, rd:vec3<f32>) -> f32{
+    let MAX_STEPS:i32 = 100;
+    let MAX_DIST:f32 = 100.0;
+    let SURF_DIST:f32 = 0.01;
+    var d:f32 = 0.0;
+    
+    var i: i32 = 0;
+    loop {
+      if(i >= MAX_STEPS){
+        break;
+      }
+
+      let p = ro + rd * d;
+      let ds = getDist(p);
+      d = d + ds;
+      if(d > MAX_DIST || ds <= SURF_DIST){
+        break;
+      } 
+
+      i = i + 1;
+    }
+    return d;
+}
+
+fn getNormal(p:vec3<f32>) -> vec3<f32>{
+    let d = getDist(p);
+    let e = vec2<f32>(0.1,0.0);
+    
+    // We can find the normal using the points around the hit point
+    let n = d - vec3<f32>(
+        getDist(p-e.xyy),
+        getDist(p-e.yxy),
+        getDist(p-e.yyx)
+      );
+        
+    return normalize(n);
+}
+
+fn getLight(p:vec3<f32>) -> f32{
+    let SURF_DIST:f32 = .01;
+
+    let light_pos = vec3<f32>(0.,5.,0.);
+    let l = normalize(light_pos - p) * 1.;
+    let n = getNormal(p);
+    
+    var dif = clamp(dot(n,l),.0,1.);
+    
+    let d = rayMarch(p + n * SURF_DIST * 2.,l);
+    if(d<length(light_pos - p)){
+        dif = dif * .1;
+    }
+    
+    return dif;
+}
+
+@stage(fragment) fn main(
+    @location(0) uv : vec2<f32>
+) -> @location(0) vec4<f32> {
+    let aspect = ubo.resolution / min(ubo.resolution.x,ubo.resolution.y);
+    let tmp_uv = (uv - vec2(0.5,0.5)) * aspect * 2.0;
+    var col = vec3<f32>(0.0);
+    
+    let r_origin = vec3<f32>(4.0,3.,.0);
+    let r_dir = normalize(vec3<f32>(-1.0,tmp_uv.y,tmp_uv.x));
+    let d = rayMarch(r_origin,r_dir);
+    col = vec3<f32>(d / 8.);
+    let p = r_origin + r_dir * d;
+    let diff = getLight(p);
+    
+    col = vec3<f32>(diff , 0.,0.);
+    return vec4<f32>(col,0.0);
+}