View Space Tri Strips Shader

draw_demo.cpp

void Arc::draw(ofxShader& shader)
{
    GLuint pr_loc = glGetAttribLocationARB(shader.shader, "a_vtx_pr");
    GLuint nx_loc = glGetAttribLocationARB(shader.shader, "a_vtx_nx");

    glColor4f(color.x, color.y, color.z, 1);
    glBegin(GL_TRIANGLE_STRIP);
    ofxVec3f vtx_pr, vtx, vtx_nx;
    vtx_nx.set(p1);
    for(int i = 1; i < n_steps; i++){
        float u = i / (n_steps - 1.0f);
        float t = u * t_pos;
        float th = thickness * ofLerp(0.5f, 1.0f, u);

        vtx_pr.set(vtx);
        vtx.set(vtx_nx);
        vtx_nx.set(
            Utilz::bezierPoint(p1.x, p2.x, p3.x, p4.x, t),
            Utilz::bezierPoint(p1.y, p2.y, p3.y, p4.y, t),
            Utilz::bezierPoint(p1.z, p2.z, p3.z, p4.z, t)
        );

        glVertexAttrib4fARB(pr_loc, vtx_pr.x, vtx_pr.y, vtx_pr.z, 1.0f);
        glVertexAttrib4fARB(nx_loc, vtx_nx.x, vtx_nx.y, vtx_nx.z, 1.0f);

    	glTexCoord3f(t * -tex_reps, 0.0f, -th);
        glVertex3f(vtx.x, vtx.y, vtx.z);

        glVertexAttrib4fARB(pr_loc, vtx_pr.x, vtx_pr.y, vtx_pr.z, 1.0f);
        glVertexAttrib4fARB(nx_loc, vtx_nx.x, vtx_nx.y, vtx_nx.z, 1.0f);

        glTexCoord3f(t * -tex_reps, 1.0f, th);
        glVertex3f(vtx.x, vtx.y, vtx.z);
    }
    glEnd();
}

viewspace_strip.frag

varying vec3 uv;

void main()
{
    gl_FragColor = gl_Color;
}

viewspace_strip.vert

attribute vec4 a_vtx_pr, a_vtx_nx;

varying vec3 uv;

void main()
{
    // Project
    vec4 vtx    = gl_ModelViewProjectionMatrix * gl_Vertex;
    vec4 vtx_pr = gl_ModelViewProjectionMatrix * a_vtx_pr;
    vec4 vtx_nx = gl_ModelViewProjectionMatrix * a_vtx_nx;

    // Get 2D Coords
    vec2 vtx2d = vtx.xy / vtx.w;
    vec2 vtx_pr2d = vtx_pr.xy / vtx_pr.w;
    vec2 vtx_nx2d = vtx_nx.xy / vtx_nx.w;

    vec2 norm2d = normalize(
    	vec2(-(vtx2d.y - vtx_pr2d.y), vtx2d.x - vtx_pr2d.x) +
        vec2(-(vtx_nx2d.y - vtx2d.y), vtx_nx2d.x - vtx2d.x)
    );

    uv = gl_MultiTexCoord0.xyz;

    gl_Position = vtx + vec4(norm2d * uv.z, 0.0, 0.0);

    gl_FrontColor = gl_Color;
    gl_BackColor = gl_Color;
}