From 6de802e7dadfc00e5a4f4af8ab9600ca9c89c9a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luis=20Pe=C3=B1aranda?= <luisp@impa.br>
Date: Wed, 14 Aug 2013 11:57:26 -0300
Subject: [PATCH] pass ZB parameters to the shader automatically

---
 openglcanvas.cpp                | 16 +++++++++++-----
 shaders/test_vertex_shader.vert | 12 ++++--------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/openglcanvas.cpp b/openglcanvas.cpp
index b18d881..82bffc1 100644
--- a/openglcanvas.cpp
+++ b/openglcanvas.cpp
@@ -709,11 +709,17 @@ void OpenGLCanvas::setShaders() {
 
     GLuint p = glCreateProgram();
 
-    // Bind attributes zblambda and zbR to the vertex shader
-    glVertexAttrib1f(0,zblambda);
-    glBindAttribLocation(p,0,"zblambda");
-    glVertexAttrib1f(1,zbR);
-    glBindAttribLocation(p,1,"zbR");
+    // Bind attributes zblambda and zbR to the vertex shader. Nvidia hardware
+    // only leaves attributes 1 and 7 unreserved; attributes 8 to 15 are
+    // reserved for textures.
+    // TODO: we use attributes 14 and 15, which work for Nvidia; we need to
+    // test with other hardware.
+#define ZBL_ATTR 14
+#define ZBR_ATTR 15
+    glVertexAttrib1f(ZBL_ATTR,zblambda);
+    glBindAttribLocation(p,ZBL_ATTR,"zblambda");
+    glVertexAttrib1f(ZBR_ATTR,zbR);
+    glBindAttribLocation(p,ZBR_ATTR,"zbR");
 
     glAttachShader(p,v);
     glAttachShader(p,f);
diff --git a/shaders/test_vertex_shader.vert b/shaders/test_vertex_shader.vert
index 6f057b2..26a58d7 100644
--- a/shaders/test_vertex_shader.vert
+++ b/shaders/test_vertex_shader.vert
@@ -6,9 +6,7 @@ float u, v, x, y, z;
 varying float r, theta, s;
 float lambda, phi;
 float extent, scale, vis_mode, center_lambda, center_phi;
-float zbr,zbalpha,zbrho;
-/*attribute*/ float zblambda;
-/*attribute*/ float zbR;
+attribute float zblambda,zbR;
 
 void main(void){
 
@@ -87,11 +85,9 @@ void main(void){
         u=x/(-z);
         v=y/(-z);
         // Z-B transformation
-        zblambda=0.1;
-        zbR=1.0;
-        zbalpha=atan(v,u);
-        zbr=sqrt(u*u+v*v);
-        zbrho=(zblambda*zbr/zbR)+(1.0-zblambda)*(zbR*(sqrt(zbr*zbr+1.0)-1.0))/(zbr*(sqrt(zbR*zbR+1.0)-1.0));
+        float zbalpha=atan(v,u);
+        float zbr=sqrt(u*u+v*v);
+        float zbrho=(zblambda*zbr/zbR)+(1.0-zblambda)*(zbR*(sqrt(zbr*zbr+1.0)-1.0))/(zbr*(sqrt(zbR*zbR+1.0)-1.0));
         u=zbrho*cos(zbalpha);
         v=zbrho*sin(zbalpha);
         gl_Position = vec4(u/extent,v/extent,z,1.0);
-- 
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