c++openglglslshadertesselation

glPolygonMode not rendering in correct mode


I recently started learning tessellation and today I was trying to draw a triangle after tessellation so that I can see all the tessellated smaller triangles using glPolygonMode(GL_FRONT_AND_BACK, GL_LINE). But for some reason the output is just a coloured background without any triangle in it. For the tessellation, I make a control shader and evaluation shader and then link them to the program.(Code below)

// Source code for Tesselation Control Shader
static const GLchar * tesselation_control_shader[] = 
{
    "#version 450 core                                  \n"
    "                                                   \n"
    "layout(vertices = 3) out;                          \n"
    "                                                   \n"
    "void main(void)                                    \n"
    "{                                                  \n"
    "   //Only if I am invocation 0                     \n"
    "   if (gl_InvocationID == 0)                       \n"
    "   {                                               \n"
    "       gl_TessLevelInner[0] = 5.0;                 \n"
    "       gl_TessLevelOuter[0] = 5.0;                 \n"
    "       gl_TessLevelOuter[1] = 5.0;                 \n"
    "       gl_TessLevelOuter[2] = 5.0;                 \n"
    "   }                                               \n"
    "                                                   \n"
    "   // Everybody copies their input to their input  \n"
    "   gl_out[gl_InvocationID].gl_Position =           \n"
    "       gl_in[gl_InvocationID].gl_Position;         \n"
    "}                                                  \n"
};

// Source code for tesselation evaluation shader
static const GLchar * tesselation_evaluation_shader[] =
{
    "#version 450 core                                          \n"
    "                                                           \n"
    "layout(triangles, equal_spacing, cw) in;                   \n"
    "                                                           \n"
    "void main(void)                                            \n"
    "{                                                          \n"
    "   gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position +  \n"
    "       gl_TessCoord.y * gl_in[1].gl_Position +             \n"
    "       gl_TessCoord.z * gl_in[2].gl_Position);             \n"
    "}                                                          \n"
};

I then call the glPolygonMode(GL_FRONT_AND_BACK, GL_LINE) in my render function right before draw the triangle using glDrawArrays(GL_TRIANGLE, 0, 3). I initially thought that the glPolygonMode was defaulting to GL_FILL but I don't think that's the issue since I am just following a book (OpenGL Superbible 7th Edition). How can I fix this?

Edit:
I have added the code of my entire program below:

GLuint compile_shaders(void)
{
    GLuint vertex_shader;
    GLuint fragment_shader;
    GLuint control_shader;
    GLuint evaluation_shader;
    GLuint program;

    // Source code for Vertex Shader
    static const GLchar * vertex_shader_source[] =
    {
        "#version 450 core                                                      \n"
        "                                                                       \n"
        "// offset and color are input vertex attribute                         \n"
        "layout (location = 0) in vec4 offset;                                  \n"
        "layout (location = 1) in vec4 color;                                   \n"
        "                                                                       \n"
        "//Declare VS_OUT as an output interface block                          \n"
        "out VS_OUT                                                             \n"
        "{                                                                      \n"
        "   vec4 color; //Send color to next stage                              \n"
        "}vs_out;                                                               \n"
        "                                                                       \n"
        "void main(void)                                                        \n"
        "{                                                                      \n"
        "   //Decalre a hardcoded array of positions                            \n"
        "   const vec4 vertices[3] = vec4[3](vec4(0.25, -0.25, 0.5, 1.0),       \n"
        "                                    vec4(-0.25, -0.25, 0.5, 1.0),      \n"
        "                                    vec4(0.25, 0.25, 0.5, 1.0));       \n"
        "                                                                       \n"
        "   //Index into our array using gl_VertexID                            \n"
        "   gl_Position = vertices[gl_VertexID] + offset;                       \n"
        "                                                                       \n"
        "//color = vec4(1.0, 0.0, 0.0, 1.0);                                    \n"
        "//Output fixed value for vs_color                                      \n"
        "vs_out.color = color;                                                  \n"
        "}                                                                      \n"
    };

    // Source code for Fragment Shader
    static const GLchar * fragment_shader_source[] =
    {
        "#version 450 core                                                              \n"
        "                                                                               \n"
        "//Declare VS_OUT as an input interface block                                   \n"
        "in VS_OUT                                                                      \n"
        "{                                                                              \n"
        "   vec4 color; //Send color to next stage                                      \n"
        "}fs_in;                                                                        \n"
        "                                                                               \n"
        "//Ouput to the framebuffer                                                     \n"
        "out vec4 color;                                                                \n"
        "                                                                               \n"
        "void main(void)                                                                \n"
        "{                                                                              \n"
        "// Simply assign the color we were given by the vertex shader to our output    \n"
        "   color = fs_in.color;                                                        \n"
        "}                                                                              \n"
    };

    // Source code for Tesselation Control Shader
    static const GLchar * tesselation_control_shader[] = 
    {
        "#version 450 core                                  \n"
        "                                                   \n"
        "layout(vertices = 3) out;                          \n"
        "                                                   \n"
        "void main(void)                                    \n"
        "{                                                  \n"
        "   //Only if I am invocation 0                     \n"
        "   if (gl_InvocationID == 0)                       \n"
        "   {                                               \n"
        "       gl_TessLevelInner[0] = 5.0;                 \n"
        "       gl_TessLevelOuter[0] = 5.0;                 \n"
        "       gl_TessLevelOuter[1] = 5.0;                 \n"
        "       gl_TessLevelOuter[2] = 5.0;                 \n"
        "   }                                               \n"
        "                                                   \n"
        "   // Everybody copies their input to their input  \n"
        "   gl_out[gl_InvocationID].gl_Position =           \n"
        "       gl_in[gl_InvocationID].gl_Position;         \n"
        "}                                                  \n"
    };

    // Source code for tesselation evaluation shader
    static const GLchar * tesselation_evaluation_shader[] =
    {
        "#version 450 core                                          \n"
        "                                                           \n"
        "layout(triangles, equal_spacing, cw) in;                   \n"
        "                                                           \n"
        "void main(void)                                            \n"
        "{                                                          \n"
        "   gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position +  \n"
        "       gl_TessCoord.y * gl_in[1].gl_Position +             \n"
        "       gl_TessCoord.z * gl_in[2].gl_Position);             \n"
        "}                                                          \n"
    };

    // Create and compiler Vertex Shader
    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, vertex_shader_source, NULL);
    glCompileShader(vertex_shader);

    // Create and compiler Fragment Shader
    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment_shader, 1, fragment_shader_source, NULL);
    glCompileShader(fragment_shader);


    // Create and compile tesselation control shader
    control_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
    glShaderSource(control_shader, 1, tesselation_control_shader, NULL);
    glCompileShader(control_shader);

    // Create and compile tesselation evaluation shader
    evaluation_shader = glCreateShader(GL_TESS_CONTROL_SHADER);
    glShaderSource(evaluation_shader, 1, tesselation_control_shader, NULL);
    glCompileShader(evaluation_shader);

    // Create program, attach shaders to it, and link it
    program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glAttachShader(program, control_shader);
    glAttachShader(program, evaluation_shader);
    glLinkProgram(program);

    // Delete shaders as program has them now
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    glDeleteShader(control_shader);
    glDeleteShader(evaluation_shader);

    return program;
};

class TesselationCSOne : public sb7::application
{
public:

    void startup()
    {
        rendering_program = compile_shaders();
        glCreateVertexArrays(1, &vertex_array_object);
        glBindVertexArray(vertex_array_object);
    }

    void shutdown()
    {
        glDeleteVertexArrays(1, &vertex_array_object);
        glDeleteProgram(rendering_program);
        glDeleteVertexArrays(1, &vertex_array_object);
    }

    // Our rendering function
    void render(double currentTime)
    {
        // Sets colour
        static const GLfloat color[] = { (float)sin(currentTime) * 0.5f + 0.5f, (float)sin(currentTime) * 0.5f + 0.5f, 0.0f, 1.0f };

        glClearBufferfv(GL_COLOR, 0, color);

        //Tell OpenGL to draw only the outlines of the resulting triangle
        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

        // Use program object we created for rendering
        glUseProgram(rendering_program);

        GLfloat attrib[] = { 1.0, 0.0, 0.0, 0.0 };/*{ (float)sin(currentTime) * 0.5f, (float)sin(currentTime) * 0.6f, 0.0f, 0.0f };*/

        // Update value of input attribute 0
        glVertexAttrib4fv(0, attrib);

        // Draw pathes for tesselation shaders
        glPatchParameteri(GL_PATCH_VERTICES, 3);
        // Draw one triangle
        glDrawArrays(GL_PATCHES, 0, 3);
    }

private:

    GLuint rendering_program;
    GLuint vertex_array_object;
};

// Only instance of DECLARE_MAIN to state entry point
DECLARE_MAIN(TesselationCSOne);

Solution

  • So after checking a lot of sources and the Superbible's code repository I realized I have a lot of unnecessary code (For example, the interface blocks in the shaders) and even quite a few mistakes (For example I had two program varibles).
    But, after fixing all that the code that produces the required output (A tessellated triangle) is:

    /**
            Program to draw a triangle with tesselation.
    **/
    #include <sb7.h>
    
    class TesselatedTriangle : public sb7::application
    {
        void init()
        {
            static const char title[] = "Tessellated Triangle";
    
            sb7::application::init();
    
            memcpy(info.title, title, sizeof(title));
        }
    
        virtual void startup()
        {
            static const char * vertex_shader_source[] =
            {
                "#version 450 core                                                 \n"
                "                                                                  \n"
                "void main(void)                                                   \n"
                "{                                                                 \n"
                "    const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0),  \n"
                "                                   vec4(-0.25, -0.25, 0.5, 1.0),  \n"
                "                                   vec4( 0.25,  0.25, 0.5, 1.0)); \n"
                "                                                                  \n"
                "    gl_Position = vertices[gl_VertexID];                          \n"
                "}                                                                 \n"
            };
    
            static const char * tesselation_control_shader_source[] =
            {
                "#version 450 core                                                                 \n"
                "                                                                                  \n"
                "layout (vertices = 3) out;                                                        \n"
                "                                                                                  \n"
                "void main(void)                                                                   \n"
                "{                                                                                 \n"
                "    if (gl_InvocationID == 0)                                                     \n"
                "    {                                                                             \n"
                "        gl_TessLevelInner[0] = 5.0;                                               \n"
                "        gl_TessLevelOuter[0] = 5.0;                                               \n"
                "        gl_TessLevelOuter[1] = 5.0;                                               \n"
                "        gl_TessLevelOuter[2] = 5.0;                                               \n"
                "    }                                                                             \n"
                "    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;     \n"
                "}                                                                                 \n"
            };
    
            static const char * tesselation_evaluation_shader_source[] =
            {
                "#version 450 core                                                                 \n"
                "                                                                                  \n"
                "layout (triangles, equal_spacing, cw) in;                                         \n"
                "                                                                                  \n"
                "void main(void)                                                                   \n"
                "{                                                                                 \n"
                "    gl_Position = (gl_TessCoord.x * gl_in[0].gl_Position) +                       \n"
                "                  (gl_TessCoord.y * gl_in[1].gl_Position) +                       \n"
                "                  (gl_TessCoord.z * gl_in[2].gl_Position);                        \n"
                "}                                                                                 \n"
            };
    
            static const char * fragment_shader_source[] =
            {
                "#version 450 core                                                 \n"
                "                                                                  \n"
                "out vec4 color;                                                   \n"
                "                                                                  \n"
                "void main(void)                                                   \n"
                "{                                                                 \n"
                "    color = vec4(0.0, 0.8, 1.0, 1.0);                             \n"
                "}                                                                 \n"
            };
    
            rendering_program = glCreateProgram();
    
            // Compile shaders
            GLuint vs = glCreateShader(GL_VERTEX_SHADER);
            glShaderSource(vs, 1, vertex_shader_source, NULL);
            glCompileShader(vs);
    
            GLuint tcs = glCreateShader(GL_TESS_CONTROL_SHADER);
            glShaderSource(tcs, 1, tesselation_control_shader_source, NULL);
            glCompileShader(tcs);
    
            GLuint tes = glCreateShader(GL_TESS_EVALUATION_SHADER);
            glShaderSource(tes, 1, tesselation_evaluation_shader_source, NULL);
            glCompileShader(tes);
    
            GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
            glShaderSource(fs, 1, fragment_shader_source, NULL);
            glCompileShader(fs);
    
            // Attach shaders to the program
            glAttachShader(rendering_program, vs);
            glAttachShader(rendering_program, tcs);
            glAttachShader(rendering_program, tes);
            glAttachShader(rendering_program, fs);
    
            // Link the program
            glLinkProgram(rendering_program);
    
            // Generate vertex arrays
            glGenVertexArrays(1, &vertex_array_object);
            glBindVertexArray(vertex_array_object);
    
            // Declare the drawing mode for the polygons
            glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
        }
    
        virtual void render(double currentTime)
        {
            static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
    
            glClearBufferfv(GL_COLOR, 0, green);
    
            glUseProgram(rendering_program);
    
            glDrawArrays(GL_PATCHES, 0, 3);
        }
    
        virtual void shutdown()
        {
            glDeleteVertexArrays(1, &vertex_array_object);
    
            glDeleteProgram(rendering_program);
        }
    
    
    private:
    
        GLuint          rendering_program;
        GLuint          vertex_array_object;
    
    };
    
    // One and only instance of DECLARE_MAIN
    DECLARE_MAIN(TesselatedTriangle)
    

    Hopefully this helps somebody else with the same problem.