Stencil Shadows

OpenGL OpenGL: Basic Coding
1

Hello!

I am creating a 3d world and for shadows i use the stencil buffer.The stencil shadows works corectly according to the light source.
The light source for now i just a red dot and i only move it right ,left , up , down and the shadows are projected corectly acording the light source.
How can i rotate the light source around my world like sun do, and the shadows follow the light ?
I alredy used translation and rotation of the red dot , but only rotates the dot and not the light.

Plz help…I can post some code if necessary…

2

Does only the dot rotate and not the light, or does the light rotate, but the shadow doesn’t? If the light reflections on the terrain don’t rotate, then there’s something wrong with your light source, and you only apply the rotation to the dot and forget to set the light position accordingly.

And yes, some code would help.

3

Here how it is…

both shadows and light works corectly when i move the light source manualy (up down left right) presing some butons …
but i want to automaticaly rotate it around my world using gltranslate… when i use gltranslate it is rotated only the light source( the light still is projected corectly) but the shadows dont move.

glPushMatrix();
glDisable(GL_LIGHTING);

glColor3f(1,0,0);
glBegin(GL_POINTS);
glVertex3f(lightPosition[0],lightPosition[1],lightPosition[2]);      // the coordinates of the light source  who creates shadows  
glEnd();




glEnable(GL_LIGHTING);
glEnable(GL_TEXTURE_2D);
glPopMatrix();
4

Could you also provide code for how the terrain is drawn, as well as the shadows? The above code doesn’t help much in finding the error. And please, use [noparse]

[/noparse] for code next time :wink:

5

this is the code for shadows , terrain ( draw world) , buildings , light source


	glMatrixMode(GL_MODELVIEW);	
	glLoadIdentity();									// Reset The Current Modelview Matrix
   

	gluLookAt(objCamera.mPos.x,  objCamera.mPos.y,  objCamera.mPos.z,	
			  objCamera.mView.x, objCamera.mView.y, objCamera.mView.z,	
			  objCamera.mUp.x,   objCamera.mUp.y,   objCamera.mUp.z);
   glRotatef(rotWorld,-1.0, 0.0, 0.0);


// Turn off writing to the Color Buffer and Depth Buffer
	// We want to draw to the Stencil Buffer only
	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
	glDepthMask(GL_FALSE);


	// Enable the Stencil Buffer
	glEnable(GL_STENCIL_TEST);

	// Set 1 into the stencil buffer
	glStencilFunc(GL_ALWAYS, 1, 0xFFFFFFFF);
	glStencilOp(GL_REPLACE, GL_REPLACE, GL_REPLACE);

	// Draw the floor
	
	DrawWorld();

	// Turn on Color Buffer and Depth Buffer
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
	glDepthMask(GL_TRUE);


	// Only write to the Stencil Buffer where 1 is set
	glStencilFunc(GL_EQUAL, 1, 0xFFFFFFFF);
	// Keep the content of the Stencil Buffer
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

	// Draw the floor

	
	DrawWorld();

	glPushMatrix();
	
	glColor4f(0.0, 0.0, 0.0, 0.3f);

	// Disable light
	glDisable(GL_TEXTURE_2D);
	glDisable(GL_LIGHTING);
	glDisable(GL_DEPTH_TEST);
	// Enable blending
	glEnable(GL_BLEND);

	glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
	// Calculate the projected shadow
	shadowmatrix(floorShadow, groundplane, lightPosition);
	glMultMatrixf((float *)floorShadow);


	DrawBuildings();
	

	glTranslatef(7,7,1.0);
	glScalef(0.1,0.1,0.1);
	Draw_Model();



	glEnable(GL_TEXTURE_2D);
	glEnable(GL_DEPTH_TEST);
	glDisable(GL_BLEND);
	glEnable(GL_LIGHTING);
	glPopMatrix();



	glPushMatrix();
	// Dissable Stencil Buffer
	glDisable(GL_STENCIL_TEST);
	glTranslatef(7,7,1.0);
	glScalef(0.1,0.1,0.1);
	Draw_Model();

	glPopMatrix();




	glPushMatrix();
	glDisable(GL_STENCIL_TEST);
	DrawBuildings();
	glPopMatrix();

	glPushMatrix();
	glDisable(GL_LIGHTING);




	glColor3f(1,0,0);
    glBegin(GL_POINTS);
	glVertex3f(lightPosition[0],lightPosition[1],lightPosition[2]);
	glEnd();
	
   

	
	glEnable(GL_LIGHTING);
	glEnable(GL_TEXTURE_2D);
	glPopMatrix();





	glPushMatrix();
	glTranslatef(lightPosition[0],lightPosition[1],lightPosition[2]);	
	
	glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, Lt0spec);	// Make sphere glow 
	glutSolidSphere(1.3, 20, 20);		
	glMaterialfv(GL_FRONT_AND_BACK, GL_EMISSION, Noemit);	// Turn off emission





	if ( LightIsPositional==1 ) {
		glLightfv(GL_LIGHT0, GL_POSITION, zeroPos );	// Position is transformed by ModelView matrix
	}
	else {
		glLightfv(GL_LIGHT0, GL_POSITION, dirI );		// Direction is transformed by ModelView matrix
	}
	glPopMatrix();






void shadowmatrix(float shadowMat[4][4], float groundplane[4], float lightpos[4])
{

  // Find the dot product between the light position vector and the ground plane normal
	float dot = groundplane[X] * lightpos[X] + groundplane[Y] * lightpos[Y] + groundplane[Z] * lightpos[Z] + groundplane[W] * lightpos[W];

	shadowMat[0][0] = dot - lightpos[X] * groundplane[X];
	shadowMat[1][0] = 0.f - lightpos[X] * groundplane[Y];
	shadowMat[2][0] = 0.f - lightpos[X] * groundplane[Z];
	shadowMat[3][0] = 0.f - lightpos[X] * groundplane[W];

	shadowMat[X][1] = 0.f - lightpos[Y] * groundplane[X];
	shadowMat[1][1] = dot - lightpos[Y] * groundplane[Y];
	shadowMat[2][1] = 0.f - lightpos[Y] * groundplane[Z];
	shadowMat[3][1] = 0.f - lightpos[Y] * groundplane[W];

	shadowMat[X][2] = 0.f - lightpos[Z] * groundplane[X];
	shadowMat[1][2] = 0.f - lightpos[Z] * groundplane[Y];
	shadowMat[2][2] = dot - lightpos[Z] * groundplane[Z];
	shadowMat[3][2] = 0.f - lightpos[Z] * groundplane[W];

	shadowMat[X][3] = 0.f - lightpos[W] * groundplane[X];
	shadowMat[1][3] = 0.f - lightpos[W] * groundplane[Y];
	shadowMat[2][3] = 0.f - lightpos[W] * groundplane[Z];
	shadowMat[3][3] = dot - lightpos[W] * groundplane[W];

}