Support logarithmic depth buffer (#199)

* Support `logarithmicDepthBuffer`

* Use `#include <logdepthbuf_pars_vertex>`

* use includes everywhere if possible or reasonable

src/shaders/splatFragment.glsl

@@ -3,6 +3,7 @@ precision highp float;
 precision highp int;
 
 #include <splatDefines>
+#include <logdepthbuf_pars_fragment>
 
 uniform float near;
 uniform float far;
@@ -93,4 +94,5 @@ void main() {
             fragColor = rgba;
         #endif
     }
+    #include <logdepthbuf_fragment>
 }

src/shaders/splatVertex.glsl

@@ -4,6 +4,7 @@ precision highp int;
 precision highp usampler2DArray;
 
 #include <splatDefines>
+#include <logdepthbuf_pars_vertex>
 
 attribute uint splatIndex;
 
@@ -35,6 +36,12 @@ uniform float focalAdjustment;
 uniform usampler2DArray packedSplats;
 uniform vec4 rgbMinMaxLnScaleMinMax;
 
+#ifdef USE_LOGDEPTHBUF
+    bool isPerspectiveMatrix( mat4 m ) {
+      return m[ 2 ][ 3 ] == - 1.0;
+    }
+#endif
+
 void main() {
     // Default to outside the frustum so it's discarded if we return early
     gl_Position = vec4(0.0, 0.0, 2.0, 1.0);
@@ -215,4 +222,5 @@ void main() {
     vSplatUv = position.xy * maxStdDev;
     vNdc = ndc;
     gl_Position = vec4(ndc.xy * clipCenter.w, clipCenter.zw);
+    #include <logdepthbuf_vertex>
 }