CODEWITHSUNDEEP
c++openglshadow
Anton
Anton

Reputation: 3036

Shadow volumes - finding a silhouette

Im working on my OpenGL task, and next stage is loading models and producing shadows using shadow volumes algorithm. I do it in 3 stages -

  1. setConnectivity - finding neighbours of each triangle and storing their indices in neigh parameter of each triangle,

  2. markVisible(float* lp) - if lp represents vector of light's position, it marks triangles as visible = true or visible = false depending on dot production of its normal vector and light position,

  3. markSilhoutte(float *lp) - marking silhouette edges and building the volume itself, extending silhouette to infinity(100 units is enough) in the direction opposite to light.

I checked all stages, and can definitely say that its all ok with first two, so the problem is in third function, which i included in my question. I use the algorithm introduced in this tutorial: http://www.3dcodingtutorial.com/Shadows/Shadow-Volumes.html

Briefly, edge is included in silhouette if it belongs to the visible triangle and non-visible triangle at the same time. Here is a pair of screenshots to show you whats wrong: http://prntscr.com/17dmg , http://prntscr.com/17dmq

As you can see, green sphere represents light's position, and these ugly green-blue polygons are faces of "shadow volume". You can also see, that im applying this function to the model of cube, and one of volume's side is missing(its not closed, but i should be). Can someone suggest whats wrong with my code and how can i fix it? Here goes the code i promised to include(variables names are self-explanatory, i suppose, but if you dont think so i can add description for each of them):

void Model::markSilhouette(float* lp){
        glBegin(GL_QUADS);
        for ( int i = 0; i < m_numMeshes; i++ )
        {
            for ( int t = 0; t < m_pMeshes[i].m_numTriangles; t++ )
            {
                int triangleIndex = m_pMeshes[i].m_pTriangleIndices[t];
                Triangle* pTri = &m_pTriangles[triangleIndex];
                if (pTri->visible){

                    for(int j=0;j<3;j++){
                        int triangleIndex = m_pMeshes[i].m_pTriangleIndices[pTri->neigh[j]-1];
                        Triangle* pTrk = &m_pTriangles[triangleIndex];
                        if(!pTrk->visible){
                            int p1j=pTri->m_vertexIndices[j];
                            int p2j=pTri->m_vertexIndices[(j+1)%3];
                            float* v1=m_pVertices[p1j].m_location;
                            float* v2=m_pVertices[p2j].m_location;

                            float x1=m_pVertices[p1j].m_location[0];
                            float y1=m_pVertices[p1j].m_location[1];
                            float z1=m_pVertices[p1j].m_location[2];

                            float x2=m_pVertices[p2j].m_location[0];
                            float y2=m_pVertices[p2j].m_location[1];
                            float z2=m_pVertices[p2j].m_location[2];

                            t=100;

                            float xl1=(x1-lp[0])*t;
                            float yl1=(y1-lp[1])*t;
                            float zl1=(z1-lp[2])*t;

                            float xl2=(x2-lp[0])*t;
                            float yl2=(y2-lp[1])*t;
                            float zl2=(z2-lp[2])*t;
                            glColor3f(0,0,1);

                            glVertex3f(x1 + xl1,
                                y1 + yl1,
                                z1 + zl1);
                            glVertex3f(x1,
                                y1,
                                z1);
                            glColor3f(0,1,0);

                            glVertex3f(x2 + xl2,
                                y2 + yl2,
                                z2 + zl2);
                            glVertex3f(x2,
                                y2,
                                z2);
                        }
                    }

                }

            }
        }
        glEnd();
    }

Upvotes: 1

Views: 1025

Answers (2)

Anton
Anton

Reputation: 3036

I've found it. It looks like if you dont see an obvious algorithm mistake for a few days, then you've made a f*cking stupid mistake.

My triangle index variable is called t. Guess what? My extending vector length is also called t, and they are in the same scope, and i set t=100 after FIRST visible triangle :D So now volumes look like this: outside http://prntscr.com/17l3n inside http://prntscr.com/17l40 And it looks good for all light positions(acceptable by shadow volumes aglorithm, of course). So the working code for drawing a shadow volume is the following: 

void Model::markSilouette(float* lp){
    glDisable(GL_LIGHTING);
    glPointSize(4.0);
    glEnable(GL_COLOR_MATERIAL);
    glColorMaterial(GL_FRONT_AND_BACK,GL_FILL);
    glBegin(GL_QUADS);
    for ( int i = 0; i < m_numMeshes; i++ )
    {
        for ( int t = 0; t < m_pMeshes[i].m_numTriangles; t++ )
        {
            int triangleIndex = m_pMeshes[i].m_pTriangleIndices[t];
            Triangle* pTri = &m_pTriangles[triangleIndex];

            if (pTri->visible){
                for(int j=0;j<3;j++){
                    Triangle* pTrk;
                    if(pTri->neigh[j]){
                        int triangleIndex = m_pMeshes[i].m_pTriangleIndices[pTri->neigh[j]-1];
                        pTrk = &m_pTriangles[triangleIndex];
                    }

                        if((!pTri->neigh[j]) || !pTrk->visible){

                            int p1j=pTri->m_vertexIndices[j];
                            int p2j=pTri->m_vertexIndices[(j+1)%3];
                            float* v1=m_pVertices[p1j].m_location;
                            float* v2=m_pVertices[p2j].m_location;

                            float x1=m_pVertices[p1j].m_location[0];
                            float y1=m_pVertices[p1j].m_location[1];
                            float z1=m_pVertices[p1j].m_location[2];

                            float x2=m_pVertices[p2j].m_location[0];
                            float y2=m_pVertices[p2j].m_location[1];
                            float z2=m_pVertices[p2j].m_location[2];

                            float f=100; // THE PROBLEM WAS HERE

                            float xl1=(x1-lp[0])*f;
                            float yl1=(y1-lp[1])*f;
                            float zl1=(z1-lp[2])*f;

                            float xl2=(x2-lp[0])*f;
                            float yl2=(y2-lp[1])*f;
                            float zl2=(z2-lp[2])*f;
                            glColor3f(0,0,0);
                            glVertex3f(x1 + xl1,
                                y1 + yl1,
                                z1 + zl1);
                            glVertex3f(x1,
                                y1,
                                z1);
                            glVertex3f(x2,
                                y2,
                                z2);
                            glVertex3f(x2 + xl2,
                                y2 + yl2,
                                z2 + zl2);
                        }
                    }
                }

        }
    }
    glEnd();
}

Upvotes: 1

shybovycha
shybovycha

Reputation: 12265

I think everything is ok, you are just rendering volume without depth test =)

Upvotes: 0

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