# OpenGL projective texture mapping

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I have recently been trying to implement some shadowing algorithms and have come unstuck trying to implement this one. The algorithm I have gathered (from various nvidia, ATI and here) for it is: -Set up an orthographic projection -Resize the viewport so that the entire terrain is within the viewing window -Transform the scene using the light's direction vector -Render all scene meshes to the screen -Copy frame buffer to a texture -Reset modelview transformation to look straight down at terrain -Render terrain using the texture we just created -Copy frame buffer to final shadow map texture making use of Render To Texture availability inside OpenGL. I have been following an example which is similar to what I want but I can't see what it wrong with my code: http://gpwiki.org/index.php/Generating_Mesh_Shadows_On_Terrain_Using_OpenGL I only seem to be getting a red quad in the bottom left hand corner of the screen and I'm not sure why.
void createProjectiveTexture(JVector3D lightDir) {

//create an Image
glEnable(GL_TEXTURE_2D);
glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 0, 0,0, 256, 256);
glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

//Set up an Orthographic Projection
//Ensure the whole scene is withing the viewing window
const int TEXTURE_MAP_SIZE = 512;
glViewport(0, 0, TEXTURE_MAP_SIZE,TEXTURE_MAP_SIZE);
glMatrixMode(GL_PROJECTION);
glOrtho(0, TEXTURE_MAP_SIZE, 0, TEXTURE_MAP_SIZE, -10000, 10000);
glMatrixMode(GL_MODELVIEW);

//Transform the scee using light vector
JVector3D lookAt(0,0,0);
JVector3D up(0,1,0);
gluLookAtv(lightDir, lookAt, up);

//Render the Scene

//  drawLightSource();
//   drawFloor();
//   drawBoundingScene();

//make sure the vertices are inside for some reason they are not
//at the moment

static GLint viewport[4];
static GLdouble modelview[16];
static GLdouble projection[16];
static GLfloat winX, winY, winZ;

float minX = 999999, maxX = -999999;
float minY = 999999, maxY = -999999;
double X, Y, Z;

glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );

//   renderVertex(-100.0,0.0,100.0);
//      glTexCoord2f(0.0,5.0);renderVertex(100.0,0.0,100.0);
//      glTexCoord2f(5.0,5.0);renderVertex(100.0,0.0,-100.0);
//      glTexCoord2f(5.0,0.0);renderVertex(-100.0,0.0,-100.0);
gluProject(100.0,0.0,100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;

gluProject(100.0,0.0,-100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;
gluProject(-100.0,0.0,-100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;
gluProject(-100.0,0.0,100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;

static float minX2, minY2, maxX2, maxY2;
minX2 = minX;
minY2 = minY;
maxX2 = maxX;
maxY2 = maxY;

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, TEXTURE_MAP_SIZE,TEXTURE_MAP_SIZE);
glMatrixMode(GL_PROJECTION);
glOrtho(minX, maxX, minY, maxY, -10000, 10000);
glMatrixMode(GL_MODELVIEW);

//glColor3f(0.0,0.0,0.0);
drawLightSource();
drawFloor();
drawBoundingScene();
drawScene(true, false, PROJECTED_TEXTURE);

//Use Render to Texture
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, TEXTURE_MAP_SIZE, TEXTURE_MAP_SIZE);
glBindTexture(GL_TEXTURE_2D, 0);
//Reset View Position to be above the center (0,0,0) along the Y Axis.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, TEXTURE_MAP_SIZE, TEXTURE_MAP_SIZE);
glMatrixMode(GL_PROJECTION);
glOrtho(0, 0, TEXTURE_MAP_SIZE, TEXTURE_MAP_SIZE, -10000, 10000);
glMatrixMode(GL_MODELVIEW);

glRotatef(90.0f, 1, 0, 0);       //Rotate so XZ becomes XY

minX = minY = 999999;
maxX = maxY = -999999;

glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );

//   renderVertex(-100.0,0.0,100.0);
//      glTexCoord2f(0.0,5.0);renderVertex(100.0,0.0,100.0);
//      glTexCoord2f(5.0,5.0);renderVertex(100.0,0.0,-100.0);
//      glTexCoord2f(5.0,0.0);renderVertex(-100.0,0.0,-100.0);
gluProject(100.0,0.0,100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;

gluProject(100.0,0.0,-100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;
gluProject(-100.0,0.0,-100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;
gluProject(-100.0,0.0,100.0, modelview, projection, viewport, &X, &Y, &Z);
if(X &lt; minX) minX = X; if(X &gt; maxX) maxX = X; if(Y &lt; minY) minY = Y;
if(Y &gt; maxY) maxY = Y;

glViewport(0, 0, 256,256);
glMatrixMode(GL_PROJECTION);
glOrtho(minX, minY, maxX, maxY, -10000, 10000);
glMatrixMode(GL_MODELVIEW);
// rotate view so that xz plane becomes the xy plane
glRotatef(90.0f, 1, 0, 0);

//Set up projective Texturing and Planes
float PS[] = {1, 0, 0, 0};
float PT[] = {0, 1, 0, 0};
float PR[] = {0, 0, 1, 0};
float PQ[] = {0, 0, 0, 1};

glTexGenfv(GL_S, GL_EYE_PLANE, PS);
glTexGenfv(GL_T, GL_EYE_PLANE, PT);
glTexGenfv(GL_R, GL_EYE_PLANE, PR);
glTexGenfv(GL_Q, GL_EYE_PLANE, PQ);

glEnable(GL_TEXTURE_GEN_S);
glEnable(GL_TEXTURE_GEN_T);
glEnable(GL_TEXTURE_GEN_R);
glEnable(GL_TEXTURE_GEN_Q);
glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_Q, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);

glMatrixMode(GL_TEXTURE);
glTranslatef(0.5, 0.5, 0);
glScalef(0.5, 0.5, 1);
glOrtho(minX2, maxX2, minY2, maxY2, -10000, 10000);
gluLookAtv(v_LightSource, lookAt, up);
glMatrixMode(GL_MODELVIEW);
drawScene(false, false, PROJECTED_TEXTURE);

//copy final image into texture

glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, TEXTURE_MAP_SIZE, TEXTURE_MAP_SIZE);

// disable TexGEN - projective texturing
glDisable(GL_TEXTURE_GEN_S);
glDisable(GL_TEXTURE_GEN_T);
glDisable(GL_TEXTURE_GEN_R);
glDisable(GL_TEXTURE_GEN_Q);

glMatrixMode(GL_TEXTURE);

glMatrixMode(GL_MODELVIEW);
}


Anybody have any ideas what could be the problem? Neutrinohunter Edit: In Code!

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