QT OpenGL, glDrawElements and glDrawArray show only blank screen - c++

Question

I'm using Qt (5.6.0) to make a dungeon crawler/rogue-like with the interface done in Qt and the gameplay scene (3D map, character, monsters..) in OpenGL. The view is a promoted QWidget and I am able to draw using the old glBegin/glEnd method but whenever I try using glDrawArrays or glDrawElements, I get a blank screen.
The clear color is working and is set to be slightly lighter than black, so a black shape should show up. I am using the glBegin/glEnd method for testing with the same vertices and it does render as it should. I have tried a more or less straight OpenGL approach as shown by Jamie King, through several more examples and tutorials, finally ending on this example for using the QOpenGLShaderProgram and QOpenGLVertexArrayObject objects along with the example in the QOpenGLShaderProgram Qt doc. Currently the shader code in the initializeGL function is preventing the glBegin/glEnd triangle from being drawn.
Current Code:
oglwidget.cpp:
#include "GL/glew.h"
#include "GL/glext.h"
#include "oglwidget.h"
#include "general.h"
#define BUFFER_OFFSET(bytes) ((GLubyte*) NULL + (bytes))
extern const char * vertexShader;
extern const char * fragmentShader;
OGLWidget::OGLWidget(QWidget *parent): QOpenGLWidget(parent){
}
OGLWidget::~OGLWidget(){
}
void OGLWidget::initializeGL(){
QOpenGLFunctions gl;
gl.initializeOpenGLFunctions();
cout<<"Init"<<endl;
//-----Create Shader
shader2.create();
shader2.addShaderFromSourceCode(QOpenGLShader::Vertex,vertexShader);
shader2.addShaderFromSourceCode(QOpenGLShader::Fragment,fragmentShader);
shader2.link();
shader2.bind();
int vertexLocation = shader2.attributeLocation("vertex");
int matrixLocation = shader2.uniformLocation("matrix");
int colorLocation = shader2.uniformLocation("color");
QMatrix4x4 pmvMatrix;
pmvMatrix.ortho(rect());
QColor color(0, 255, 0, 255);
shader2.enableAttributeArray(vertexLocation);
shader2.setAttributeArray(vertexLocation, verts, 3);
shader2.setUniformValue(matrixLocation, pmvMatrix);
shader2.setUniformValue(colorLocation, color);
//-----Create VAO2
VAO2=new QOpenGLVertexArrayObject(this);
VAO2->create();
VAO2->bind();
//-----Create VBO2
VBO2.create();
VBO2.setUsagePattern(QOpenGLBuffer::StaticDraw);
VBO2.bind();
VBO2.allocate(verts,sizeof(verts));
}
void OGLWidget::paintGL(){
cout<<"Painting"<<endl;
QOpenGLFunctions gl;
gl.initializeOpenGLFunctions();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glClearColor(0.05,0.05,0.05,1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f,0.0f,-2.0f);
//draw();
shader2.bind();
VAO2->bind();
glDrawElements(GL_TRIANGLES,3,GL_UNSIGNED_INT,inds);
VAO2->release();
}
void OGLWidget::resizeGL(int w, int h){
cout<<"Resizing"<<endl;
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
//glFrustum (-1.0, 1.0, -1.0, 1.0, 1, 1000.0); //-----Assuming this is right?
glOrtho(-5,5,-5,5,-5,5);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
int OGLWidget::loadModel(string path){
//-----loads the model path if not already loaded, returns the index of the model
//---check if already loaded
for(int p=0;p<loadedPaths.size();p++){
if(!loadedPaths[p].compare(path)){
return p;
}
}
loadedPaths.push_back(path);
//-----continue with path loading
Model m;
m.loadModel(path);
return loadedPaths.size()-1;
}
void OGLWidget::draw(){
cout<<"drawing..."<<endl;
glBegin(GL_TRIANGLES);
for(int i=0;i<sizeof(verts)/sizeof(GLfloat);i+=3){
//cout<<i<<endl;
glVertex3f(verts[i],verts[i+1],verts[i+2]);
}
glEnd();
}
oglwidget.h:
#ifndef OGLWIDGET_H
#define OGLWIDGET_H
#include <QWidget>
#include <QOpenGLWidget>
#include <glm/glm.hpp>
#include <QOpenGLFunctions>
#include <vector>
#include "entity.h"
#include "general.h"
#include <qopenglfunctions_3_3_core.h>
//#include <GL/glu.h>
//#include <GL/gl.h>
#define VERTEXATTR 0
#define INDEXATTR 1
#define POSITIONATTR 2
#define ROTATIONATTR 3
using namespace std;
class OGLWidget : public QOpenGLWidget
{
//QOpenGLFunctions gl;
//QOpenGLFunctions_3_3_Core core;
QOpenGLVertexArrayObject *VAO2;
QOpenGLBuffer VBO2;
QOpenGLShaderProgram shader2;
QOpenGLContext *m_context;
vector<GLuint>statics; //-----buffer number for static models
vector<GLuint>dynamics; //-----buffer number of dynamic models
vector<GLfloat[1]>staticVerts; //-----vertex data for static models
vector<GLfloat[1]>dynamicVerts; //-----vertex data for dynamic models
vector<vector<GLfloat>*>staticPos; //-----position data for static models
vector<vector<GLfloat>*>dynamicPos; //-----position data for dynamic models
vector<GLfloat>staticRot; //-----rotation data for static models
vector<GLfloat>dynamicRot; //-----rotation data for dynamic models
vector<string>loadedPaths; //-----name in folder of matching VBO
GLuint VBO;
GLuint IND;
GLuint FragID;
GLuint VertID;
GLuint shader;
//-----Testing
GLfloat verts[9]={-1.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f,
1.0f, 0.0f, 0.0f};
GLuint inds[3]={0,1,2};
public:
OGLWidget(QWidget *parent = 0);
~OGLWidget();
int loadModel(string path);
private:
void draw();
QGLShaderProgram m_shader;
QGLBuffer m_vertexBuffer;
protected:
void initializeGL();
void resizeGL(int w, int h);
void paintGL();
};
#endif // OGLWIDGET_H
shader.cpp:
const char * vertexShader=
"attribute highp vec4 vertex;\n"
"uniform highp mat4 matrix;\n"
"void main(void)\n"
"{\n"
" gl_Position = matrix * vertex;\n"
"}";
const char * fragmentShader=
"uniform mediump vec4 color;\n"
"void main(void)\n"
"{\n"
" gl_FragColor = color;\n"
"}";
From what I've read (correct me if I'm wrong) the objective it to load the vertex, color, texture and other data to the GPU memory using a VAO, rebind the VAO before drawing, draw using glDrawArrays or glDrawElements and release the VAO. Using the indexed version of the function will allow for changes in position, scale and rotation, meaning faster rendering for larger quantities of the same object (ie. the game tiles) and GL_STATIC_DRAW should be used for objects that are not updated frequently, with GL_DYNAMIC_DRAW for everything else.
I'm wanting to know what I'm missing or doing wrong with what really should be a simple exercise. I've redone this at least 5 times over and am at a complete loss.
OS: Debian Testing
GPU: GeForce 610m
OpenGL Core: 3.3
Qt: 5.6
Software: Qt Creator

Answer 1

Solution thanks to #PeterT in the comments: move the shader enableAttributeArray and setAttributeBuffer (changed from setAttributeArray)to after the VBO allocation and modify the vertex coordinates and ortho to be 'larger'.
void OGLWidget::initializeGL()
{
QOpenGLFunctions gl;
gl.initializeOpenGLFunctions();
glDisable(GL_CULL_FACE);
cout<<"Init"<<endl;
shader2.create();
shader2.addShaderFromSourceCode(QOpenGLShader::Vertex,vertexShader);
shader2.addShaderFromSourceCode(QOpenGLShader::Fragment,fragmentShader);
shader2.link();
shader2.bind();
int vertexLocation = shader2.attributeLocation("vertex");
int matrixLocation = shader2.uniformLocation("matrix");
int colorLocation = shader2.uniformLocation("color");
QMatrix4x4 pmvMatrix;
//pmvMatrix.ortho(rect());
pmvMatrix.ortho(-100,100,-100,100,-1000,1000);
QColor color(0, 255, 0, 255);
shader2.enableAttributeArray(vertexLocation);
shader2.setUniformValue(matrixLocation, pmvMatrix);
shader2.setUniformValue(colorLocation, color);
//-----Create VAO2
VAO2=new QOpenGLVertexArrayObject(this);
VAO2->create();
VAO2->bind();
VBO2.create();
VBO2.setUsagePattern(QOpenGLBuffer::StaticDraw);
VBO2.bind();
VBO2.allocate(verts,sizeof(verts));
shader2.enableAttributeArray("vertex");
shader2.setAttributeBuffer("vertex",GL_FLOAT,0,3,0);
}
*
GLfloat verts[9]={-100.0f, 0.0f, 30.0f,
0.0f, 100.0f, 50.0f,
100.0f, 0.0f, 30.0f};