I have a problem with trying to render a glucylinder between two 3d points.
Based on the code from here
This seems to work for all cases except when the cylinder is aligned to the Y axis. ie from (0,-5,0) to (0,+5,0). In that case the Y axis aligned cylinder either flickers (like its rotation is being flipped around each frame) or it renders from the first point out in space the opposite direction to the second point.
Can anyone help with the right “if then” code to fix the Y axis problem? I have done a lot of searching on these forums and the web trying to find working code. It will definitely help me and I am sure others who come here looking for the solution in the future.
procedure CylinderGL(p1,p2:point3d;r1,r2:double;precision:integer); var quadratic:pGLUquadricObj; height,dx,dy,dz:double; v,vx,vy,vz,rx,ry,rz,zero,ax,r2d:double; begin r2d:=180/pi; //length of cylinder dx:=p1.x-p2.x; dy:=p1.y-p2.y; dz:=p1.z-p2.z; height:=sqrt(dx*dx+dy*dy+dz*dz); glpushmatrix; gltranslatef(p1.x,p1.y,p1.z); //now rotate the matrix into position // orientation vectors vx:=p2.x-p1.x; // component in x-direction vy:=p2.y-p1.y; // component in y-direction vz:=p2.z-p1.z; // component in z-direction v:=sqrt(vx*vx+vy*vy+vz*vz); // cylinder length // rotation vector, z x r rx:=-vy*vz; ry:=+vx*vz; ax:=0.0; if vz=0 then begin ax:=r2d*arccos(vx/v); // rotation angle in x-y plane if vx<=0 then ax:=-ax; end else begin ax:=r2d*arccos(vz/v); // rotation angle if vz<=0 then ax:=-ax; end; if vz=0 then begin glRotated(90.0, 0, 1, 0.0); // Rotate & align with x axis glRotated(ax, -1.0, 0.0, 0.0); // Rotate to point 2 in x-y plane end else begin glRotated(ax, rx, ry, 0.0); // Rotate about rotation vector end; quadratic:=gluNewQuadric; // Create A Pointer To The Quadric Object ( NEW ) gluQuadricNormals(quadratic, GLU_SMOOTH); // Create Smooth Normals ( NEW ) gluQuadricTexture(quadratic, FALSE); // Create Texture Coords ( NEW ) gluCylinder(quadratic,r1,r2,height,precision,precision); // Draw A cylinder glpopmatrix; end;