Use shifted invZ for Z to keep precision

GL/draw.c

@@ -939,12 +939,25 @@ GL_FORCE_INLINE void divide(SubmissionTarget* target) {
     /* Perform perspective divide on each vertex */
     Vertex* vertex = _glSubmissionTargetStart(target);
 
+    /* PVR expects with invW or invZ as the final depth coordinate,
+     * but there are issues with that. Using invW means that orthographic
+     * projections fail (because W is always 1). invZ fails when stuff is near
+     * the near plane (because it ends up <= 0) so what we do is take invZ
+     * and add the near-plane distance (plus an epsilon value) to take it above 0
+     * then invert that. */
+
+    Matrix4x4* proj = _glGetProjectionMatrix();
+    float m22 = (*proj)[10];
+    float m32 = (*proj)[14];
+    float zNear = MATH_Fast_Divide((2.0f * m32), (2.0f * m22 - 2.0f));
+
     ITERATE(target->count) {
         float f = MATH_Fast_Invert(vertex->w);
         vertex->xyz[0] *= f;
         vertex->xyz[1] *= f;
-        vertex->xyz[2] *= f;
-        vertex->xyz[2] = PVR_MAX_Z - ((vertex->xyz[2] + 1.0f) * 0.5f);
+        vertex->xyz[2] = MATH_Fast_Invert(
+            vertex->xyz[2] + zNear + 0.05f
+        );
         ++vertex;
     }
 }