OpenGL Cube in C++ - c++

Question

I am having some issues trying to rendering a cube using OpenGL and C++. I was able to get a simple square on the screen, after adding the extra vertices, a slightly tilted triangle was shown instead... Now I have tried to use an element buffer. I filled the element_buffer [] with extra values (I admittedly found on a tutorial) and have nothing being displayed. Any help would be great.
#include "CubeAsset.h"
CubeAsset::CubeAsset() {
// model coordinates, origin at centre.
GLfloat vertex_buffer [] {
-0.5f,-0.5f,-0.5f, // triangle 0 : begin
-0.5f,-0.5f, 0.5f,
-0.5f, 0.5f, 0.5f, // triangle 0 : end
0.5f, 0.5f,-0.5f, // triangle 2 : begin
-0.5f,-0.5f,-0.5f,
-0.5f, 0.5f,-0.5f, // triangle 2 : end
0.5f,-0.5f, 0.5f,
-0.5f,-0.5f,-0.5f,
0.5f,-0.5f,-0.5f,
0.5f, 0.5f,-0.5f,
0.5f,-0.5f,-0.5f,
-0.5f,-0.5f,-0.5f,
-0.5f,-0.5f,-0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f, 0.5f,-0.5f,
0.5f,-0.5f, 0.5f,
-0.5f,-0.5f, 0.5f,
-0.5f,-0.5f,-0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f,-0.5f, 0.5f,
0.5f,-0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
0.5f,-0.5f,-0.5f,
0.5f, 0.5f,-0.5f,
0.5f,-0.5f,-0.5f,
0.5f, 0.5f, 0.5f,
0.5f,-0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
0.5f, 0.5f,-0.5f,
-0.5f, 0.5f,-0.5f,
0.5f, 0.5f, 0.5f,
-0.5f, 0.5f,-0.5f,
-0.5f, 0.5f, 0.5f,
0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, 0.5f,
0.5f,-0.5f, 0.5f
};
element_buffer_length = 36;
GLubyte element_buffer [] {
0, 1, 2, 2, 3, 0,
0, 3, 4, 4, 5, 0,
0, 5, 6, 6, 1, 0,
1, 6, 7, 7, 2, 1,
7, 4, 3, 3, 2, 7,
4, 7, 6, 6, 5, 4
};
// Transfer buffers to the GPU
//
// create buffer
glGenBuffers(1, &vertex_buffer_token);
// immediately bind the buffer and transfer the data
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_token);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 12, vertex_buffer, GL_STATIC_DRAW);
glGenBuffers(1, &element_buffer_token);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, element_buffer_token);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * element_buffer_length, element_buffer, GL_STATIC_DRAW);
}
CubeAsset::~CubeAsset() {
}
#ifdef DEBUG
#define checkGLError() checkError(__FILE__, __LINE__)
#else
// define symbol to be nothing
#define checkGLError()
#endif
void checkError(std::string file, int line) {
GLenum gl_error = glGetError();
if(GL_NO_ERROR != gl_error) {
std::cerr << "GL error in " << file << " at line " << line << " error: " << gl_error << std::endl;
exit(-1);
}
}
void CubeAsset::Draw(GLuint program_token) {
if(!glIsProgram(program_token)) {
std::cerr << "Drawing Cube with invalid program" << std::endl;
return;
}
GLint validation_ok;
glValidateProgram(program_token);
glGetProgramiv(program_token, GL_VALIDATE_STATUS, &validation_ok);
if(!validation_ok) {
GLint maxLength = 0;
glGetProgramiv(program_token, GL_INFO_LOG_LENGTH, &maxLength);
//The maxLength includes the NULL character
std::vector<char> errorLog(maxLength);
glGetProgramInfoLog(program_token, maxLength, &maxLength, &errorLog[0]);
std::cerr << "Invalid program " << program_token << " with error code " << validation_ok << std::endl;
for(auto c: errorLog) {
std::cerr << c;
}
exit(-1);
}
GLuint position_attrib = glGetAttribLocation(program_token, "position");
checkGLError();
glUseProgram(program_token);
checkGLError();
// use the previously transferred buffer as the vertex array. This way
// we transfer the buffer once -- at construction -- not on every frame.
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_token);
glVertexAttribPointer(
position_attrib, /* attribute */
3, /* size */
GL_FLOAT, /* type */
GL_FALSE, /* normalized? */
0, /* stride */
(void*)0 /* array buffer offset */
);
glEnableVertexAttribArray(position_attrib);
checkGLError();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, element_buffer_token);
glDrawElements(
GL_TRIANGLES,
element_buffer_length,
GL_UNSIGNED_INT,
(GLvoid*) 0
);
checkGLError();
glDisableVertexAttribArray(position_attrib);
}
The header file:
#ifndef CUBEASSET_H
#define CUBEASSET_H
#include <vector>
#include <GL/gl.h>
#include <glm/glm.hpp>
#include <glm/ext.hpp>
#include "GameAsset.h"
class CubeAsset : public GameAsset {
public:
CubeAsset();
~CubeAsset();
virtual void Draw(GLuint);
private:
GLuint element_buffer_length;
GLuint vertex_buffer_token, element_buffer_token;
};
#endif // CUBEASSET_H

Answer 1

You have a type mismatch. You indices in your code are of type GLubyte:
GLubyte element_buffer [] {
0, 1, 2, 2, 3, 0,
...
But the rest of the code treats the as GLuint:
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * element_buffer_length, ...);
...
glDrawElements(GL_TRIANGLES, element_buffer_length, GL_UNSIGNED_INT, ...);
You need to settle on using a consistent type, either GLubyte everywhere, or GLuint everywhere.