OpenGL issue: cannot render geometry on screen

Question

My program was meant to draw a simple textured cube on screen, however, I cannot get it to render anything other than the clear color. This is my draw function:

    void testRender() {
    glClearColor(.25f, 0.35f, 0.15f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glUniformMatrix4fv(resources.uniforms.m4ModelViewProjection, 1, GL_FALSE, (const GLfloat*)resources.modelviewProjection.modelViewProjection);
    glEnableVertexAttribArray(resources.attributes.vTexCoord);
    glEnableVertexAttribArray(resources.attributes.vVertex);
    //deal with vTexCoord first
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,resources.hiBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, resources.htcBuffer);
    glVertexAttribPointer(resources.attributes.vTexCoord,2,GL_FLOAT,GL_FALSE,sizeof(GLfloat)*2,(void*)0);
    //now the other one
    glBindBuffer(GL_ARRAY_BUFFER,resources.hvBuffer);
    glVertexAttribPointer(resources.attributes.vVertex,3,GL_FLOAT,GL_FALSE,sizeof(GLfloat)*3,(void*)0);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, resources.htextures[0]);
    glUniform1i(resources.uniforms.colorMap, 0);
    glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_SHORT, (void*)0);
    //clean up a bit
};

In addition, here is the vertex shader:

#version 330

in vec3 vVertex;
in vec2 vTexCoord;

uniform mat4 m4ModelViewProjection;

smooth out vec2 vVarryingTexCoord;

void main(void) {
    vVarryingTexCoord = vTexCoord;
    gl_Position = m4ModelViewProjection * vec4(vVertex, 1.0);
};

and the fragment shader (I have given up on textures for now):

#version 330

uniform sampler2D colorMap;

in vec2 vVarryingTexCoord;
out vec4 vVaryingFragColor;
void main(void) {
vVaryingFragColor = texture(colorMap, vVarryingTexCoord);
vVaryingFragColor = vec4(1.0,1.0,1.0,1.0);
};

the vertex array buffer for the position coordinates make a simple cube (with all coordinates a signed 0.25) while the modelview projection is just the inverse camera matrix (moved back by a factor of two) applied to a perspective matrix. However, even without the matrix transformation, I am unable to see anything onscreen. Originally, I had two different buffers that needed two different element index lists, but now both buffers (containing the vertex and texture coordinate data) are the same length and in order. The code itself is derived from the Durian Software Tutorial and the latest OpenGL Superbible. The rest of the code is here.

By this point, I have tried nearly everything I can think of. Is this code even remotely close? If so, why can't I get anything to render onscreen?

Tim Tim · Accepted Answer · 2012-08-24T21:13:50

You're looking pretty good so far.

The only thing that I see right now is that you've got DEPTH_TEST enabled, but you don't clear the depth buffer. Even if the buffer initialized to a good value, you would be drawing empty scenes on every frame after the first one, because the depth buffer's not being cleared.

If that does not help, can you make sure that you have no glGetError() errors? You may have to clean up your unused texturing attributes/uniforms to get the errors to be clean, but that would be my next step.

OpenGL issue: cannot render geometry on screen

1 Answers