I have a situation where I want all of the objects in my landscape to be static while I move a “camera” around. Thus far I have done this, but when I implement shadows they don’t stay with the landscape as I move. When the program first starts out and I haven’t moved the shadows are fine. But when I move the shadows move too; they sort of move with me, but not completely. Here’s what I do (if you’re familiar with NeHe’s tutorials it is adapted from that)
int DrawGLScene(GLvoid) // Here’s Where We Do All The Drawing
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT); // Clear The Screen And The Depth Buffer
glLoadIdentity(); // Reset The ViewGLfloat x_m, y_m, z_m, u_m, v_m, nx, ny, nz;
GLfloat width, depth;
GLfloat radius, height, bangle, eangle, divisions;
int sangle, arclength, division, face;
GLfloat xtrans = -xpos; //Set the x-axis position by the opposite (move camera not scene) of the incriment designated by pressing the key
GLfloat ztrans = -zpos; //“” with z-axis
GLfloat ytrans = -0.5f-ypos; //bounce up and down as if walking
GLfloat sceneroty = 360.0f - yrot;
GLfloat newlightpos[4];GLmatrix16f Minv;
GLvector4f lp;int numtrans, looptrans;
float numquads, numcyls, numcubics, numdiscs;
float tx = 0;
float ty = 0;
float tz = 0;
float magnitude = 0;
float rx = 0;
float ry = 0;
float rz = 0;
long textureaddress;glRotatef(lookupdown, 1.0f, 0.0f, 0.0f); //Enables looking up and down on x-axis
glRotatef(sceneroty, 0.0f, 1.0f, 0.0f); //Enables left and right turning on y-axisglTranslatef(xtrans, ytrans, ztrans); //Move to new position after changing by increment
//create light source
glTranslatef (l_x, l_y, l_z);
glColor4f(0.7f, 0.4f, 0.0f, 1.0f);glDisable (GL_LIGHTING);
gluSphere (quadratic, 0.05f, 32, 32);
glEnable(GL_LIGHTING); // Enable LightingglLightfv(GL_LIGHT1, GL_POSITION,LightPosition); // Position The Light
newlightpos[0] = LightPosition[0] + l_x; // store new light position
newlightpos[1] = LightPosition[1] + l_y; // " "
newlightpos[2] = LightPosition[2] + l_z; // " "
newlightpos[3] = LightPosition[3];
glTranslatef (-l_x, -l_y, -l_z);numquads = sector1.numquads; //Set number of quadrilaterals into temporary variable in order to work with it
// process quadrilaterals
for (int loopquad = 0; loopquad < numquads; ++loopquad)
{
numtrans = sector1.quad[loopquad].transnum + 1;
for (looptrans = 0; looptrans < numtrans; ++looptrans)
{glPushMatrix(); if (looptrans) { tx = sector1.quad[loopquad].trans[looptrans - 1].x; ty = sector1.quad[loopquad].trans[looptrans - 1].y; tz = sector1.quad[loopquad].trans[looptrans - 1].z; glTranslatef (tx, ty, tz); } textureaddress = sector1.quad[loopquad].textureaddy; glBindTexture (GL_TEXTURE_2D, texture[textureaddress]); glBegin(GL_QUADS); nx = sector1.quad[loopquad].nx; ny = sector1.quad[loopquad].ny; nz = sector1.quad[loopquad].nz; for (int loopvertex = 0; loopvertex < 4; ++loopvertex) { x_m = sector1.quad[loopquad].vertex[loopvertex].x; y_m = sector1.quad[loopquad].vertex[loopvertex].y; z_m = sector1.quad[loopquad].vertex[loopvertex].z; u_m = sector1.quad[loopquad].vertex[loopvertex].u; v_m = sector1.quad[loopquad].vertex[loopvertex].v; glNormal3f(nx, ny, nz); glTexCoord2f(u_m, v_m); glVertex3f(x_m, y_m, z_m); } glEnd(); lp[0] = newlightpos[0]; // Store Light Position X In lp[0] lp[1] = newlightpos[1]; // Store Light Position Y In lp[1] lp[2] = newlightpos[2]; // Store Light Position Z In lp[2] lp[3] = newlightpos[3]; // Store Light Direction In lp[3] castShadow (sector1.quad[loopquad].vertex[0], sector1.quad[loopquad].vertex[1], sector1.quad[loopquad].vertex[2], sector1.quad[loopquad].vertex[3], lp); glPopMatrix(); }}
glFlush();
return TRUE;
}//this part does the shadows
void doShadowPass (const VERTEX& c_v1, const VERTEX& c_v2, const VERTEX& c_v3, const VERTEX& c_v4, GLfloat *lightPosition)
{
VERTEX v3, v4;//go through each edge
//edge 1
//edge vertices
const VERTEX& v1 = c_v1;
const VERTEX& v2 = c_v2;
//distant vertices
v3.x = (v1.x - lightPosition[0]) * INFINITY;
v3.y = (v1.y - lightPosition[1]) * INFINITY;
v3.z = (v1.z - lightPosition[2]) * INFINITY;v4.x = (v2.x - lightPosition[0]) * INFINITY;
v4.y = (v2.y - lightPosition[1]) * INFINITY;
v4.z = (v2.z - lightPosition[2]) * INFINITY;//draw resultant quadrilateral
glBegin (GL_TRIANGLE_STRIP);
glVertex3f( v1.x, v1.y, v1.z );
glVertex3f( v1.x+v3.x, v1.y+v3.y, v1.z+v3.z );
glVertex3f( v2.x, v2.y, v2.z );
glVertex3f( v2.x+v4.x, v2.y+v4.y, v2.z+v4.z );
glEnd();
//edge 2
//edge vertices
const VERTEX& v1_2 = c_v2;
const VERTEX& v2_2 = c_v3;
//distant vertices
v3.x = (v1_2.x - lightPosition[0]) * INFINITY;
v3.y = (v1_2.y - lightPosition[1]) * INFINITY;
v3.z = (v1_2.z - lightPosition[2]) * INFINITY;v4.x = (v2_2.x - lightPosition[0]) * INFINITY;
v4.y = (v2_2.y - lightPosition[1]) * INFINITY;
v4.z = (v2_2.z - lightPosition[2]) * INFINITY;//draw resultant quadrilateral
glBegin (GL_TRIANGLE_STRIP);
glVertex3f( v1_2.x, v1_2.y, v1_2.z );
glVertex3f( v1_2.x+v3.x, v1_2.y+v3.y, v1_2.z+v3.z );
glVertex3f( v2_2.x, v2_2.y, v2_2.z );
glVertex3f( v2_2.x+v4.x, v2_2.y+v4.y, v2_2.z+v4.z );
glEnd();
//edge 3
//edge vertices
const VERTEX& v1_3 = c_v3;
const VERTEX& v2_3 = c_v4;
//distant vertices
v3.x = (v1_3.x - lightPosition[0]) * INFINITY;
v3.y = (v1_3.y - lightPosition[1]) * INFINITY;
v3.z = (v1_3.z - lightPosition[2]) * INFINITY;v4.x = (v2_3.x - lightPosition[0]) * INFINITY;
v4.y = (v2_3.y - lightPosition[1]) * INFINITY;
v4.z = (v2_3.z - lightPosition[2]) * INFINITY;//draw resultant quadrilateral
glBegin (GL_TRIANGLE_STRIP);
glVertex3f( v1_3.x, v1_3.y, v1_3.z );
glVertex3f( v1_3.x+v3.x, v1_3.y+v3.y, v1_3.z+v3.z );
glVertex3f( v2_3.x, v2_3.y, v2_3.z );
glVertex3f( v2_3.x+v4.x, v2_3.y+v4.y, v2_3.z+v4.z );
glEnd();//edge 4
//edge vertices
const VERTEX& v1_4 = c_v4;
const VERTEX& v2_4 = c_v1;
//distant vertices
v3.x = (v1_4.x - lightPosition[0]) * INFINITY;
v3.y = (v1_4.y - lightPosition[1]) * INFINITY;
v3.z = (v1_4.z - lightPosition[2]) * INFINITY;v4.x = (v2_4.x - lightPosition[0]) * INFINITY;
v4.y = (v2_4.y - lightPosition[1]) * INFINITY;
v4.z = (v2_4.z - lightPosition[2]) * INFINITY;//draw resultant quadrilateral
glBegin (GL_TRIANGLE_STRIP);
glVertex3f( v1_4.x, v1_4.y, v1_4.z );
glVertex3f( v1_4.x+v3.x, v1_4.y+v3.y, v1_4.z+v3.z );
glVertex3f( v2_4.x, v2_4.y, v2_4.z );
glVertex3f( v2_4.x+v4.x, v2_4.y+v4.y, v2_4.z+v4.z );
glEnd();
}void castShadow (const VERTEX& v1, const VERTEX& v2, const VERTEX& v3, const VERTEX& v4, GLfloat *lightPosition)
{
GLfloat a, b, c, d, side;
bool visible;//calculate plane equation in the form: ax + by + cz + d
a = v1.y*(v2.z-v3.z) + v2.y*(v3.z-v1.z) + v3.y*(v1.z-v2.z);
b = v1.z*(v2.x-v3.x) + v2.z*(v3.x-v1.x) + v3.z*(v1.x-v2.x);
c = v1.x*(v2.y-v3.y) + v2.x*(v3.y-v1.y) + v3.x*(v1.y-v2.y);
d = -( v1.x*( v2.yv3.z - v3.yv2.z ) + v2.x*(v3.yv1.z - v1.yv3.z) + v3.x*(v1.yv2.z - v2.yv1.z) );side = alightPosition[0]+
blightPosition[1]+
c*lightPosition[2]+
d;if (side > 0)
visible = true;
else
visible = false;//Preserve attributes that get changed
glPushAttrib( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_ENABLE_BIT | GL_POLYGON_BIT | GL_STENCIL_BUFFER_BIT );glDisable( GL_LIGHTING ); // Turn Off Lighting
glDepthMask( GL_FALSE ); // Turn Off Writing To The Depth-Buffer
glDepthFunc( GL_LEQUAL );glEnable( GL_STENCIL_TEST ); // Turn On Stencil Buffer Testing
glColorMask( GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE ); // Don’t Draw Into The Colour Buffer
glStencilFunc( GL_ALWAYS, 1, 0xFFFFFFFFL );if (visible)
{
//first shadow pass
glFrontFace( GL_CCW );
glStencilOp( GL_KEEP, GL_KEEP, GL_INCR );
doShadowPass( v1, v2, v3, v4, lightPosition );// second shadow pass. Decrease stencil value in the shadow glFrontFace( GL_CW ); glStencilOp( GL_KEEP, GL_KEEP, GL_DECR ); doShadowPass( v1, v2, v3, v4, lightPosition );}
glFrontFace( GL_CCW );
glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE ); // Enable rendering to colour buffer for all components// Draw A Shadowing Rectangle Covering The Entire Screen
glColor4f( 0.0f, 0.0f, 0.0f, 0.4f );
glEnable( GL_BLEND );
glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );
glStencilFunc( GL_NOTEQUAL, 0, 0xFFFFFFFFL );
glStencilOp( GL_KEEP, GL_KEEP, GL_KEEP );
glPushMatrix();
glLoadIdentity();
glBegin( GL_TRIANGLE_STRIP );
glVertex3f(-0.1f, 0.1f,-0.10f);
glVertex3f(-0.1f,-0.1f,-0.10f);
glVertex3f( 0.1f, 0.1f,-0.10f);
glVertex3f( 0.1f,-0.1f,-0.10f);
glEnd();
glPopMatrix();
glPopAttrib();
}
I’m still fairly new at this, so don’t be surprised at the inefficiency. Basically the program loads in a text file and stores it into object classes (the code above has been simplified). When drawing, it translates the camera when keys are pressed, then it shifts to optional duplications of an object and then draws it. After that the shadow is drawn. One of these translations is causing the shadows to move for some reason but I am not sure why.