GtkGLArea not drawing colours from fragment shader; C++

anon112 · 04-17-2016, 09:06 AM

I've mostly worked with GLFW in the past, however a recent project required me to implement an OpenGL draw area in a GTK. Configuring my rendering and shaders are all the same, the only real difference is that I'm setting up a GtkGLArea widget to handle my draw calls instead of a GLFW window.

I've built my UI using glade and I'm packing my GtkGLArea into a Paned window element within a Paned window element. As a test program I decided to try drawing a simple coloured triangle with a dark red background. However, whenever I try to render anything drawn with glDrawArrays(...), I just get a black silhouette of what I'm trying to draw. Even if I modify my fragment shader to only draw white, it draws black.

Fragment shader:

Code:

#version 330 core

in vec3 VertCol;
out vec4 color;

void main()
{
    //color = vec4(VertCol.xyz,1.0f);
    color = vec4(1.0f,1.0f,1.0f,1.0f);
}

Initializing my GtkGLArea:

Code:

//(in main)
gtk_builder_add_from_file(Builder,"GladeInterface.glade",NULL);
Win = gtk_builder_get_object(Builder,"RootWindow");
GObject* GLDrawArea = (GObject*)gtk_gl_area_new();
gtk_gl_area_set_required_version((GtkGLArea*)GLDrawArea,3,3);
ERR = g_signal_connect(GLDrawArea,"realize",G_CALLBACK(GLAreaRealize),NULL);
if (ERR < 0) fprintf(stderr,"[OpenGL]: Unable to realize OpenGL context\n");
ERR = g_signal_connect(GLDrawArea,"render",G_CALLBACK(GLAreaRender),NULL);
if (ERR < 0) fprintf(stderr,"[OpenGL]: Unable to initialize OpenGL render\n");
GObject* EventBox = gtk_builder_get_object(Builder,"EventBox");
gtk_container_add((GtkContainer*)EventBox,(GtkWidget*)GLDrawArea);
gtk_widget_show(GTK_WIDGET(Win));
gtk_widget_show((GtkWidget*)GLDrawArea);

"realize" and "render" callbacks:

Code:

void GLAreaRender(GtkGLArea *area, GdkGLContext *context, gpointer data)
{
    glClearColor (0.5f, 0.0f, 0.0f, 1.0f);
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //Draw Functions Go Here
    glUseProgram(GLB_Shader.ProgID);
    glBindVertexArray(GLB_VAO);
    glBindBuffer(GL_ARRAY_BUFFER,GLB_VBO);
    GLfloat PN[] = {1.0f,1.0f,-1.0f,    1.0f,1.0f,1.0f,    -1.0f,-1.0f,0.0f,    0.5f,0.5f,0.5f,    0.3f,1.0f,0.3f,    0.3f,0.3f,0.3f};
    glBufferData(GL_ARRAY_BUFFER,sizeof(PN),PN,GL_STATIC_DRAW);
    glDrawArrays(GL_TRIANGLES,0,3);
    glFinish();
}

void GLAreaRealize(GtkGLArea* A,gpointer data)
{
    gtk_gl_area_set_has_depth_buffer(A,1);
    gtk_gl_area_set_has_alpha(A,0);
    gtk_gl_area_set_auto_render(A,0);

    gtk_gl_area_attach_buffers(A);

    if (gtk_gl_area_get_error (A) != NULL)
    {
        fprintf(stderr,"Could not initialize OpenGL Area\n");
        return;
    }

    GLenum Shaders[2] = {GL_VERTEX_SHADER,GL_FRAGMENT_SHADER};

    gtk_gl_area_make_current(A);

    //standard GL program builder tested with other projects
    GLB_Shader.BuildProgram("Shader",Shaders,2);

    glGenVertexArrays(1,&GLB_VAO);

    glGenBuffers(1,&GLB_VBO);
    glGenBuffers(1,&GLB_EBO);
    glBindBuffer(GL_ARRAY_BUFFER,GLB_VBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,GLB_EBO);

    glBindVertexArray(GLB_VAO);
    glVertexAttribPointer(0,3,GL_FLOAT,GL_FALSE,6*sizeof(GLfloat),(GLvoid*)0);
    glVertexAttribPointer(1,3,GL_FLOAT,GL_FALSE,6*sizeof(GLfloat),(GLvoid*)(3*sizeof(GLfloat)));
    glEnableVertexAttribArray(0); //Vert Position
    glEnableVertexAttribArray(1); //Vert colour
};

I know my render code works fine with GLFW, so my buffers and shaders are both fine. The issue would seem to be related to how GTK is handling the window. Does anyone know why I can't seem to get colours to draw on a GtkGLArea?

Note: this error persists even if I make a window in code without using the builder. The gtk-demo for GtkGLArea works fine. The output I get from this code though is just a red screen with a black triangle (and from my fragment shader, the triangle should be white)