Does image affect shadow mapping?

OpenGL OpenGL: Basic Coding
1

I displayed a background image using gluOrtho2D before placing some objects in. When i tried shadow mapping, the objects are all in shadow. When i remove the background image, they are lit again. Is there a way to display the image without affecting the other objects?

I tried glOrtho() and then glrasterpos3i(), but no image is displayed.

Thanks!

2

Can you give more details about :

  • how do you draw your image ?
  • how do you get the shadow map ?
3

The image is grabbed from a camera and displayed via glDrawPixels() and gluOrtho2D().

To get the depth map, texture projection and the extensions in “extgl.h” are used. The code shown below:

//First pass - from light’s point of view
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_PROJECTION);
glLoadMatrixf(lightProjectionMatrix);

glMatrixMode(GL_MODELVIEW);
glLoadMatrixf(lightViewMatrix);

//Use viewport the same size as the shadow map
glViewport(0, 0,shadowMapSize , shadowMapSize);

DisplayImage();
//Draw back faces into the shadow map
glCullFace(GL_FRONT);

//Disable color writes, and use flat shading for speed
glShadeModel(GL_FLAT);
glColorMask(0, 0, 0, 0);

//Draw the scene
DrawScene();

//Read the depth buffer into the shadow map texture
glBindTexture(GL_TEXTURE_2D, shadowMapTexture);
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0,shadowMapSize , shadowMapSize);

//restore states
glCullFace(GL_BACK);
glShadeModel(GL_SMOOTH);
glColorMask(1, 1, 1, 1);

//2nd pass - Draw from camera’s point of view
glClear(GL_DEPTH_BUFFER_BIT);

glMatrixMode(GL_PROJECTION);
glLoadMatrixf(cameraProjectionMatrix);

glMatrixMode(GL_MODELVIEW);
glLoadMatrixf(cameraViewMatrix);

glViewport(0, 0, windowWidth, windowHeight);

//Use dim light to represent shadowed areas
glLightfv(GL_LIGHT1, GL_POSITION, VECTOR4D(lightPosition));
glLightfv(GL_LIGHT1, GL_AMBIENT, white0.2f);
glLightfv(GL_LIGHT1, GL_DIFFUSE, white0.2f);
glLightfv(GL_LIGHT1, GL_SPECULAR, black);
glEnable(GL_LIGHT1);
glEnable(GL_LIGHTING);

DrawScene();

//3rd pass
//Draw with bright light
glLightfv(GL_LIGHT1, GL_DIFFUSE, white);
glLightfv(GL_LIGHT1, GL_SPECULAR, white);

//Calculate texture matrix for projection
//This matrix takes us from eye space to the light’s clip space
//It is postmultiplied by the inverse of the current view matrix when specifying texgen
static MATRIX4X4 biasMatrix(0.5f, 0.0f, 0.0f, 0.0f,0.0f, 0.5f, 0.0f, 0.0f,0.0f, 0.0f, 0.5f, 0.0f, 0.5f, 0.5f, 0.5f, 1.0f); //bias from [-1, 1] to [0, 1]

MATRIX4X4 textureMatrix=biasMatrixlightProjectionMatrixlightViewMatrix;

//Set up texture coordinate generation.
glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGenfv(GL_S, GL_EYE_PLANE, textureMatrix.GetRow(0));
glEnable(GL_TEXTURE_GEN_S);

glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGenfv(GL_T, GL_EYE_PLANE, textureMatrix.GetRow(1));
glEnable(GL_TEXTURE_GEN_T);

glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGenfv(GL_R, GL_EYE_PLANE, textureMatrix.GetRow(2));
glEnable(GL_TEXTURE_GEN_R);

glTexGeni(GL_Q, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGenfv(GL_Q, GL_EYE_PLANE, textureMatrix.GetRow(3));
glEnable(GL_TEXTURE_GEN_Q);

//Bind & enable shadow map texture
glBindTexture(GL_TEXTURE_2D, shadowMapTexture);
glEnable(GL_TEXTURE_2D);

//Enable shadow comparison
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE_ARB, GL_COMPARE_R_TO_TEXTURE);

//Shadow comparison should be true (ie not in shadow) if r<=texture
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC_ARB, GL_LEQUAL);

//Shadow comparison should generate an INTENSITY result
glTexParameteri(GL_TEXTURE_2D, GL_DEPTH_TEXTURE_MODE_ARB, GL_INTENSITY);

//Set alpha test to discard false comparisons
glAlphaFunc(GL_GEQUAL, 0.99f);
glEnable(GL_ALPHA_TEST);

DrawScene();

//Disable textures and texgen
glDisable(GL_TEXTURE_2D);

glDisable(GL_TEXTURE_GEN_S);
glDisable(GL_TEXTURE_GEN_T);
glDisable(GL_TEXTURE_GEN_R);
glDisable(GL_TEXTURE_GEN_Q);

//Restore other states
glDisable(GL_LIGHTING);
glDisable(GL_ALPHA_TEST);

//Update frames per second counter
fpsCounter.Update();

//Print fps
static char fpsString[32];
sprintf(fpsString, "%.2f", fpsCounter.GetFps());

//Set matrices for ortho
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluOrtho2D(-1.0f, 1.0f, -1.0f, 1.0f);

glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();

When i display the image from camera, most of the light appears to be blocked.

4

This looks like the code for shadowmaps from pauls tutorials page. ( http://www.paulsprojects.net/tutorials/smt/smt.html )
I tried to use this myself and run into problems.

if you notice, between the end of the second pass
and the start of the 3rd pass there is no glClear(GL_DEPTH_BUFFER_BIT); and there is no goPolygonOffset(…,…); glEnable(GL_POLYGOn_OFFSET_FILL);

so no wonder the lighting stage fails to render (due to the depth test failin?!).
what is also weird is that Pauls code works!
what are we missing? any idea guys?
what