From d3e3112fdd478aae35da79c61686dc9fffbd6e31 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= <tastyfish@seznam.cz>
Date: Sat, 1 Jun 2019 18:49:43 +0200
Subject: [PATCH] Fix z-test bug

---
 small3dlib.h | 12 ++++++++----
 testSDL.c    |  2 ++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/small3dlib.h b/small3dlib.h
index a4bbfc2..8ef3cce 100644
--- a/small3dlib.h
+++ b/small3dlib.h
@@ -167,6 +167,10 @@
                             triangles. */
 #endif
 
+#if S3L_PERSPECTIVE_CORRECTION
+#define S3L_COMPUTE_DEPTH 1  // PC inevitably computes depth, so enable it
+#endif
+
 typedef int32_t S3L_Unit;    /**< Units of measurement in 3D space. There is
                                   S3L_FRACTIONS_PER_UNIT in one spatial unit.
                                   By dividing the unit into fractions we
@@ -1522,7 +1526,10 @@ void S3L_drawTriangle(
         p.x = x;
 
 #if S3L_COMPUTE_DEPTH
-  #if S3L_PERSPECTIVE_CORRECTION != 1
+  #if S3L_PERSPECTIVE_CORRECTION == 1
+        p.depth = (S3L_FRACTIONS_PER_UNIT * S3L_FRACTIONS_PER_UNIT) /
+          S3L_nonZero(S3L_interpolate(lRecipZ,rRecipZ,x - lX,rX - lX));
+  #else
         p.depth = S3L_getFastLerpValue(depthFLS);
         S3L_stepFastLerp(depthFLS);
   #endif
@@ -1539,9 +1546,6 @@ void S3L_drawTriangle(
 #endif
 
 #if S3L_PERSPECTIVE_CORRECTION == 1
-        p.depth = (S3L_FRACTIONS_PER_UNIT * S3L_FRACTIONS_PER_UNIT) /
-          S3L_nonZero(S3L_interpolate(lRecipZ,rRecipZ,x - lX,rX - lX));
-
         *barycentric0 =
          ( 
            S3L_interpolateFrom0(rOverZ,i,rowLength)
diff --git a/testSDL.c b/testSDL.c
index 9ca7109..4e8d1bd 100644
--- a/testSDL.c
+++ b/testSDL.c
@@ -152,6 +152,8 @@ else
 
   setPixel(p->x,p->y,col * 120,dep,(2 - col) * 120);
 
+// setPixel(p->x,p->y,  (p->triangleID * 60) % 255, (p->triangleID * 170) % 255, (p->triangleID * 10) % 255 );
+
 //setPixel(p->x,p->y,sss, (p->triangleID * 37) % 255 ,128);
 
 //setPixel(p->x,p->y,p->modelID * 64,p->modelID * 128,255);