Experimenting with tessellation subdivision formula:

using dot product for backface culling as a parameter of camera-to-face distance and angle.
Also includes face area as a parameter: the larger the face, the more subdivisions it'll need.
Visualizing this with colors, blended with the lighting data.

qmath.h

@@ -17,4 +17,11 @@ INLINE short m_pointPlaneDist2(const VECTOR point2, const SVECTOR normal12, int
     return (short)(x + y + z - dist2);
 }
 
+INLINE void m_lightColor(const CVECTOR *color, short light, CVECTOR *outColor)
+{
+    outColor->r = (uint8_t)((light * color->r) >> 8);
+    outColor->g = (uint8_t)((light * color->g) >> 8);
+    outColor->b = (uint8_t)((light * color->b) >> 8);
+}
+
 #endif // __QMATH_H__

world.c

@@ -22,6 +22,8 @@ static CVECTOR colors[] =
 };
 static const int numColors = sizeof(colors) / sizeof(CVECTOR);
 
+CVECTOR color_white = { 255, 255, 255 };
+
 // Set data pointers directly from an in-memory byte buffer
 #define LOAD_CHUNK(type, dst, num, src, entry)   \
     dst = (type*)((src) + (entry).offset);  \
@@ -49,7 +51,7 @@ void world_load(const u_long *data, world_t *world)
     LOAD_CHUNK(u_char, world->visData, world->numVisData, bytes, header->visData);
 }
 
-static INLINE void drawface_triangle_fan(const ps1bsp_face_t *face, SVECTOR *vecs)
+static INLINE void drawface_triangle_fan(const ps1bsp_face_t *face, SVECTOR *vecs, CVECTOR *color)
 {
     int p;
 
@@ -80,16 +82,16 @@ static INLINE void drawface_triangle_fan(const ps1bsp_face_t *face, SVECTOR *vec
         setPolyG3(poly);
         gte_stsxy3_g3(poly);
 
-        poly->r0 = poly->g0 = poly->b0 = (uint8_t)v0->pad;
-        poly->r1 = poly->g1 = poly->b1 = (uint8_t)v1->pad;
-        poly->r2 = poly->g2 = poly->b2 = (uint8_t)v2->pad;
+        m_lightColor(color, v0->pad, (CVECTOR*)&poly->r0);
+        m_lightColor(color, v1->pad, (CVECTOR*)&poly->r1);
+        m_lightColor(color, v2->pad, (CVECTOR*)&poly->r2);
 
         addPrim(curOT + depth, poly);
         ++polyCount;
     }
 }
 
-static INLINE void drawface_triangle_strip(const ps1bsp_face_t *face, SVECTOR *vecs)
+static INLINE void drawface_triangle_strip(const ps1bsp_face_t *face, SVECTOR *vecs, CVECTOR *color)
 {
     int p;
 
@@ -136,16 +138,16 @@ static INLINE void drawface_triangle_strip(const ps1bsp_face_t *face, SVECTOR *v
         setPolyG3(poly);
         gte_stsxy3_g3(poly);
 
-        poly->r0 = poly->g0 = poly->b0 = (uint8_t)v0->pad;
-        poly->r1 = poly->g1 = poly->b1 = (uint8_t)v1->pad;
-        poly->r2 = poly->g2 = poly->b2 = (uint8_t)v2->pad;
+        m_lightColor(color, v0->pad, (CVECTOR*)&poly->r0);
+        m_lightColor(color, v1->pad, (CVECTOR*)&poly->r1);
+        m_lightColor(color, v2->pad, (CVECTOR*)&poly->r2);
 
         addPrim(curOT + depth, poly);
         ++polyCount;
     }
 }
 
-static INLINE void drawface_quad_strip(const ps1bsp_face_t *face, SVECTOR *vecs)
+static INLINE void drawface_quad_strip(const ps1bsp_face_t *face, SVECTOR *vecs, CVECTOR *color)
 {
     int p;
 
@@ -193,10 +195,10 @@ static INLINE void drawface_quad_strip(const ps1bsp_face_t *face, SVECTOR *vecs)
         gte_rtps();
         gte_stsxy(&poly->x3);
 
-        poly->r0 = poly->g0 = poly->b0 = (uint8_t)v0->pad;
-        poly->r1 = poly->g1 = poly->b1 = (uint8_t)v1->pad;
-        poly->r2 = poly->g2 = poly->b2 = (uint8_t)v2->pad;
-        poly->r3 = poly->g3 = poly->b3 = (uint8_t)v3->pad;
+        m_lightColor(color, v0->pad, (CVECTOR*)&poly->r0);
+        m_lightColor(color, v1->pad, (CVECTOR*)&poly->r1);
+        m_lightColor(color, v2->pad, (CVECTOR*)&poly->r2);
+        m_lightColor(color, v3->pad, (CVECTOR*)&poly->r3);
 
         addPrim(curOT + depth, poly);
         ++polyCount;
@@ -237,6 +239,16 @@ static void world_drawface(const world_t *world, const ps1bsp_face_t *face)
     if ((dot >= 0) ^ face->side)
         return;
 
+    // Experimenting with tessellation levels
+    dot = abs(dot) / center.pad;// for a more stable albeit less accurate result, divide by a fixed value of 160
+    char tess;
+    if (dot < 4)
+        tess = 0;
+    else if (dot < 12)
+        tess = 1;
+    else
+        tess = 2;
+
     SVECTOR *vecs = (SVECTOR*)(scratchpad + 256);
 
     // Copy this face's vertices into scratch RAM for fast reuse
@@ -250,9 +262,9 @@ static void world_drawface(const world_t *world, const ps1bsp_face_t *face)
     }
 
     if (face->numFaceVertices == 3) // Special case: draw single triangles using the simplest method
-        drawface_triangle_fan(face, vecs);
+        drawface_triangle_fan(face, vecs, &colors[tess]);
     else
-        drawface_quad_strip(face, vecs);
+        drawface_quad_strip(face, vecs, &colors[tess]);
 }
 
 static void world_drawnode(const world_t *world, short nodeIdx, u_char *pvs)