From ffa9cae11cbe5b4565bc756da4804b9fbd999d8f Mon Sep 17 00:00:00 2001
From: timoore <timoore>
Date: Mon, 23 Nov 2009 21:53:56 +0000
Subject: [PATCH] New tree rendering algorithm

Draw trees in two passes, opaque and transparent. This allows us to
have some transparency, which is better looking, and dispense with
sorting.


Author: Tim Moore <timoore@redhat.com>
---
 Effects/tree.eff  | 61 ++++++++++++++++++++++++++++++++++++++++-------
 Shaders/tree.vert |  1 -
 2 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/Effects/tree.eff b/Effects/tree.eff
index 6713511e7..ae0e7839f 100644
--- a/Effects/tree.eff
+++ b/Effects/tree.eff
@@ -1,6 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!-- Effects files for trees, which are placed by a shader. -->
 
+<!-- Trees are drawn in two passes. The first draws the opaque parts
+     with z writes enabled. The second draws the the transparent bits
+     with z testing enabled and z writes disabled. The transparent
+     tree silhouettes will blend correctly against the opaque
+     geometry. They may cause artifacts when blending against other
+     edges, but the overall "forest" is supposed to be nice and
+     fuzzy. There might also be artifacts when blending over other
+     transparent objects, but that's mostly unavoidable.
+
+     Note: no sorting needed! -->
 <PropertyList>
   <name>Effects/tree</name>
   <parameters>
@@ -17,20 +27,16 @@
         </less-equal>
       </and>
     </predicate>
-    <pass>
+    <pass n="0">
       <lighting>true</lighting>
       <material>
         <ambient type="vec4d">1.0 1.0 1.0 1.0</ambient>
         <diffuse type="vec4d">1.0 1.0 1.0 1.0</diffuse>
         <color-mode>off</color-mode>
       </material>
-      <render-bin>
-        <bin-number>2</bin-number> <!-- RANDOM_OBJECTS_BIN -->
-        <bin-name>DepthSortedBin</bin-name>
-      </render-bin>
       <alpha-test>
         <comparison>gequal</comparison>
-        <reference type="float">0.33</reference>
+        <reference type="float">1.0</reference>
       </alpha-test>
       <texture-unit>
         <unit>0</unit>
@@ -48,9 +54,46 @@
         <type>sampler-2d</type>
         <value type="int">0</value>
       </uniform>
-      <!-- The vertex shader isn't doing two-sided lighting yet, but
-           should be soon. -->
-      <vertex-program-two-side type="bool">true</vertex-program-two-side>
+    </pass>
+    <pass n="1">
+      <lighting>true</lighting>
+      <material>
+        <ambient type="vec4d">1.0 1.0 1.0 1.0</ambient>
+        <diffuse type="vec4d">1.0 1.0 1.0 1.0</diffuse>
+        <color-mode>off</color-mode>
+      </material>
+      <render-bin>
+        <bin-number>2</bin-number> <!-- RANDOM_OBJECTS_BIN -->
+        <bin-name>RenderBin</bin-name>
+      </render-bin>
+      <alpha-test>
+        <comparison>less</comparison>
+        <!-- <reference type="float">0.33</reference>   -->
+        <reference type="float">1.0</reference>
+      </alpha-test>
+      <blend>
+        <source>src-alpha</source>
+        <destination>one-minus-src-alpha</destination>
+      </blend>
+      <depth>
+        <write-mask>false</write-mask>
+      </depth>
+      <texture-unit>
+        <unit>0</unit>
+        <type>2d</type>
+        <image><use>texture[0]/image</use></image>
+        <wrap-s>clamp</wrap-s>
+        <wrap-t>clamp</wrap-t>
+      </texture-unit>
+      <program>
+        <vertex-shader>Shaders/tree.vert</vertex-shader>
+        <fragment-shader>Shaders/tree.frag</fragment-shader>
+      </program>
+      <uniform>
+        <name>baseTexture</name>
+        <type>sampler-2d</type>
+        <value type="int">0</value>
+      </uniform>
     </pass>
   </technique>
 </PropertyList>
diff --git a/Shaders/tree.vert b/Shaders/tree.vert
index 4c5017243..8b098175e 100644
--- a/Shaders/tree.vert
+++ b/Shaders/tree.vert
@@ -29,7 +29,6 @@ void main(void)
   vec3 diffuse = gl_FrontMaterial.diffuse.rgb * max(0.1, n);
   vec4 ambientColor = gl_FrontLightModelProduct.sceneColor + gl_LightSource[0].ambient * gl_FrontMaterial.ambient;
   gl_FrontColor = ambientColor + gl_LightSource[0].diffuse * vec4(diffuse, 1.0);
-  gl_BackColor = gl_FrontColor;
 
   float fogCoord = abs(ecPosition.z);
   fogFactor = exp( -gl_Fog.density * gl_Fog.density * fogCoord * fogCoord);