From 6a3250cad28b7c5825f0b9fb1e8616ae165907a5 Mon Sep 17 00:00:00 2001
From: Gregory Hainaut <gregory.hainaut@gmail.com>
Date: Sat, 25 Apr 2015 20:23:26 +0200
Subject: [PATCH] gsdx-ogl: fix logz management (FFXII)

The issue is that z+1 overflow if z is UINT max
log2(z) overflow if z is 0

So let's use an or 1 to avoid both overflow
---
 plugins/GSdx/res/glsl/tfx_vgs.glsl | 11 +++++++++--
 plugins/GSdx/res/glsl_source.h     | 11 +++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/plugins/GSdx/res/glsl/tfx_vgs.glsl b/plugins/GSdx/res/glsl/tfx_vgs.glsl
index ae9d78d048..3a92a20165 100644
--- a/plugins/GSdx/res/glsl/tfx_vgs.glsl
+++ b/plugins/GSdx/res/glsl/tfx_vgs.glsl
@@ -116,6 +116,13 @@ void vs_main()
     else
         z = i_z;
 
+    if(VS_LOGZ == 1) {
+		// FIXME some games (FFX12 intro) uses MAX_INT as depth parameter. So I replace the +1 with an OR
+		// Initially a +1 was done to avoid log2(0) (If I'm correct)
+		// The or mask won't create any overflow
+		z |= 1u;
+	}
+
     // pos -= 0.05 (1/320 pixel) helps avoiding rounding problems (integral part of pos is usually 5 digits, 0.05 is about as low as we can go)
     // example: ceil(afterseveralvertextransformations(y = 133)) => 134 => line 133 stays empty
     // input granularity is 1/16 pixel, anything smaller than that won't step drawing up/left by one pixel
@@ -127,13 +134,13 @@ void vs_main()
     p.w = 1.0f;
 #ifdef ZERO_TO_ONE_DEPTH
     if(VS_LOGZ == 1) {
-        p.z = log2(float(1u+z)) / 32.0f;
+        p.z = log2(float(z)) / 32.0f;
     } else {
         p.z = float(z) * exp_min32;
     }
 #else
     if(VS_LOGZ == 1) {
-        p.z = log2(float(1u+z)) / 31.0f - 1.0f;
+        p.z = log2(float(z)) / 31.0f - 1.0f;
     } else {
         p.z = float(z) * exp_min31 - 1.0f;
     }
diff --git a/plugins/GSdx/res/glsl_source.h b/plugins/GSdx/res/glsl_source.h
index 335fa60315..45284af96a 100644
--- a/plugins/GSdx/res/glsl_source.h
+++ b/plugins/GSdx/res/glsl_source.h
@@ -567,6 +567,13 @@ static const char* tfx_vgs_glsl =
 	"    else\n"
 	"        z = i_z;\n"
 	"\n"
+	"    if(VS_LOGZ == 1) {\n"
+	"		// FIXME some games (FFX12 intro) uses MAX_INT as depth parameter. So I replace the +1 with an OR\n"
+	"		// Initially a +1 was done to avoid log2(0) (If I'm correct)\n"
+	"		// The or mask won't create any overflow\n"
+	"		z |= 1u;\n"
+	"	}\n"
+	"\n"
 	"    // pos -= 0.05 (1/320 pixel) helps avoiding rounding problems (integral part of pos is usually 5 digits, 0.05 is about as low as we can go)\n"
 	"    // example: ceil(afterseveralvertextransformations(y = 133)) => 134 => line 133 stays empty\n"
 	"    // input granularity is 1/16 pixel, anything smaller than that won't step drawing up/left by one pixel\n"
@@ -578,13 +585,13 @@ static const char* tfx_vgs_glsl =
 	"    p.w = 1.0f;\n"
 	"#ifdef ZERO_TO_ONE_DEPTH\n"
 	"    if(VS_LOGZ == 1) {\n"
-	"        p.z = log2(float(1u+z)) / 32.0f;\n"
+	"        p.z = log2(float(z)) / 32.0f;\n"
 	"    } else {\n"
 	"        p.z = float(z) * exp_min32;\n"
 	"    }\n"
 	"#else\n"
 	"    if(VS_LOGZ == 1) {\n"
-	"        p.z = log2(float(1u+z)) / 31.0f - 1.0f;\n"
+	"        p.z = log2(float(z)) / 31.0f - 1.0f;\n"
 	"    } else {\n"
 	"        p.z = float(z) * exp_min31 - 1.0f;\n"
 	"    }\n"