From f14855296485250277a7216c711eb598148d8346 Mon Sep 17 00:00:00 2001
From: Aaron Fenyes <aaron.fenyes@fareycircles.ooo>
Date: Thu, 29 Aug 2024 15:01:38 -0700
Subject: [PATCH] Ray-caster: only draw the top few fragments

This seems to increase graphics pipe use from 50--60% to 55--65%.
---
 .../inversive-display/src/inversive.frag      | 31 ++++++++++---------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/app-proto/inversive-display/src/inversive.frag b/app-proto/inversive-display/src/inversive.frag
index 7eb16b5..2fcd86e 100644
--- a/app-proto/inversive-display/src/inversive.frag
+++ b/app-proto/inversive-display/src/inversive.frag
@@ -25,10 +25,10 @@ vecInv sphere(vec3 center, float radius) {
 
 // construction. the SPHERE_MAX array size seems to affect frame rate a lot,
 // even though we should only be using the first few elements of each array
-const int SPHERE_MAX_UNIFORM = 200;
+const int SPHERE_MAX = 200;
 uniform int sphere_cnt;
-uniform vecInv sphere_list[SPHERE_MAX_UNIFORM];
-uniform vec3 color_list[SPHERE_MAX_UNIFORM];
+uniform vecInv sphere_list[SPHERE_MAX];
+uniform vec3 color_list[SPHERE_MAX];
 
 // view
 uniform vec2 resolution;
@@ -135,8 +135,8 @@ void main() {
     vec3 dir = vec3(focal_slope * scr, -1.);
     
     // cast rays through the spheres
-    const int SPHERE_MAX_INTERNAL = 6;
-    taggedFrag frags [2*SPHERE_MAX_INTERNAL];
+    const int LAYER_MAX = 12;
+    taggedFrag frags [LAYER_MAX];
     int layer_cnt = 0;
     for (int id = 0; id < sphere_cnt; ++id) {
         // find out where the ray hits the sphere
@@ -144,17 +144,20 @@ void main() {
         
         // insertion-sort the fragments we hit into the fragment list
         for (int side = 0; side < 2; ++side) {
-            if (hit_depths[side] > 0.) {
+            float hit_z = -hit_depths[side];
+            if (0. > hit_z) {
                 for (int layer = layer_cnt; layer >= 0; --layer) {
-                    if (layer < 1 || frags[layer-1].pt.z >= -hit_depths[side]) {
+                    if (layer < 1 || frags[layer-1].pt.z >= hit_z) {
                         // we're not as close to the screen as the fragment
                         // before the empty slot, so insert here
-                        frags[layer] = sphere_shading(
-                            sphere_list[id],
-                            hit_depths[side] * dir,
-                            color_list[id],
-                            id
-                        );
+                        if (layer < LAYER_MAX) {
+                            frags[layer] = sphere_shading(
+                                sphere_list[id],
+                                hit_depths[side] * dir,
+                                color_list[id],
+                                id
+                            );
+                        }
                         break;
                     } else {
                         // we're closer to the screen than the fragment before
@@ -163,7 +166,7 @@ void main() {
                         frags[layer] = frags[layer-1];
                     }
                 }
-                ++layer_cnt;
+                layer_cnt = min(layer_cnt + 1, LAYER_MAX);
             }
         }
     }