vertices not being drawn in opengl - c++

Question

I've been having trouble drawing a simple vertex-specified (box-like) teapot model using shaders with some input for translation and rotation. I've checked my gl code and matrices (object position on -z, camera at origin, etc) over and over and don't see why I'm still just getting a blank screen. to keep the code short, I've just put in the code for the basic cube of my model (once I at least get that I'll be fine).
namespace TeapotViewer{
class TeapotViewer{
private:
void intitialize();
void draw();
void reshape(int h, int w);
void keyHandle(unsigned char key, int x, int y);
void initCamera();
void reset();
void changeAxis();
void rotateOnAxis(float rot);
int createCube(int i);
public:
};
}
#include "TeapotViewer.h"
using namespace glm;
const int S_WIDTH = 800;
const int S_HEIGHT = 600;
const float FOV = 100;
const float P_NEAR = 0.2;
const float P_FAR = 20.0;
const float SPOUT_WIDTH = 0.025;
const float HANDLE_WIDTH = 0.15;
const float ZERO = 0.0;
const int numberOfVertices = 104;
const int noCubeSide = 10;
const int noCubeFace = 4;
const int noLine = 2;
mat4 modelxViewMatrix, projMatrix, viewMatrix, rotationMatrix, translationMatrix;
vec3 rotationAxis;
vec3 teapotPosition = vec3(0.0, 0.0,-3.0);
const vec3 cameraPosition = vec3(0.0, 0.0, 0.0);
const vec3 cameraDirection = vec3(0.0, 0.0, -1.0);
const vec3 cameraUp = vec3(0.0, 1.0, 0.0);
vec4 vertices[numberOfVertices];
GLuint refVertexArray;
GLuint refVertexBuffer;
GLuint refUniformModelxView;
GLuint refUniformProjection;
const vec4 body[] = {
vec4(-1.0,-1.0, 1.0, 1.0), vec4(-1.0, 1.0, 1.0, 1.0),
vec4( 1.0,-1.0, 1.0, 1.0), vec4( 1.0, 1.0, 1.0, 1.0),
vec4( 1.0,-1.0,-1.0, 1.0), vec4( 1.0, 1.0,-1.0, 1.0),
vec4(-1.0,-1.0,-1.0, 1.0), vec4(-1.0, 1.0,-1.0, 1.0)
};
const vec3 xAxis = vec3(1.0, 0.0, 0.0);
const vec3 yAxis = vec3(0.0, 1.0, 0.0);
const vec3 zAxis = vec3(0.0, 0.0, 1.0);
// draw callback
void draw(){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
translationMatrix = translate(mat4(), teapotPosition);
modelxViewMatrix = viewMatrix*translationMatrix*rotationMatrix;
glUniformMatrix4fv(refUniformModelxView, 1, &modelxViewMatrix[0][0]);
glUniformMatrix4fv(refUniformProjection, 1, &projMatrix[0][0]);
void drawTeapot();
glutSwapBuffers();
}
void drawTeapot(){
int bufferIndex = 0;
// draw cube
glDrawArrays(GL_TRIANGLE_STRIP, bufferIndex, noCubeSide);
bufferIndex += noCubeSide;
glDrawArrays(GL_TRIANGLE_STRIP, bufferIndex, noCubeFace);
bufferIndex += noCubeFace;
glDrawArrays(GL_TRIANGLE_STRIP, bufferIndex, noCubeFace);
bufferIndex += noCubeFace;
// draw the axis of rotation
if (rotationAxis == xAxis){
glDrawArrays(GL_LINES, bufferIndex, noLine);
bufferIndex += noLine;
}
if (rotationAxis == yAxis){
bufferIndex += noLine;
glDrawArrays(GL_LINES, bufferIndex, noLine);
bufferIndex += noLine;
}
if (rotationAxis == zAxis){
bufferIndex += noLine*2;
glDrawArrays(GL_LINES, bufferIndex, noLine);
bufferIndex += noLine;
}
}
// reset back to the start
void reset(){
teapotPosition = vec3(0.0, 0.0,-3.0);
rotationMatrix = mat4();
}
void changeAxis(){
if(rotationAxis == xAxis)
rotationAxis = yAxis;
else
if(rotationAxis == yAxis)
rotationAxis = zAxis;
else
rotationAxis = xAxis;
}
void rotateOnAxis(float rot){
rotationMatrix = rotate(rotationMatrix, rot, rotationAxis);
}
// handle keypress
void keyHandle(unsigned char key, int x, int y){
switch(key){
case 033:
exit(EXIT_SUCCESS);
break;
case '0':
reset();
break;
case 'a':
teapotPosition = teapotPosition + vec3(-0.1, 0.0, 0.0);
break;
case 'd':
teapotPosition = teapotPosition + vec3(0.1, 0.0, 0.0);
break;
case 'w':
teapotPosition = teapotPosition + vec3(0.0, 0.1, 0.0);
break;
case 's':
teapotPosition = teapotPosition + vec3(0.0, -0.1, 0.0);
break;
case 'q':
teapotPosition = teapotPosition + vec3(0.0, 0.0, -0.1);
break;
case 'e':
teapotPosition = teapotPosition + vec3(0.0, 0.0, 0.1);
break;
case 'j':
changeAxis();
break;
case 'k':
rotateOnAxis(-5.0);
break;
case 'l':
rotateOnAxis(5.0);
break;
}
glutPostRedisplay();
}
void reshape(int h, int w){
glViewport(0, 0, h, w);
}
void initCamera(){
viewMatrix = lookAt(cameraDirection, cameraPosition, cameraUp);
projMatrix = perspective(FOV, (float)S_WIDTH/(float)S_HEIGHT, P_NEAR, P_FAR);
reset();
}
int createCube(int i){
// sides of the cube
vertices[i++] = body[0];
vertices[i++] = body[1];
vertices[i++] = body[2];
vertices[i++] = body[3];
vertices[i++] = body[4];
vertices[i++] = body[5];
vertices[i++] = body[6];
vertices[i++] = body[7];
vertices[i++] = body[0];
vertices[i++] = body[1];
// top
vertices[i++] = body[0];
vertices[i++] = body[2];
vertices[i++] = body[4];
vertices[i++] = body[6];
//bottom
vertices[i++] = body[1];
vertices[i++] = body[3];
vertices[i++] = body[5];
vertices[i++] = body[7];
std::cout << i << '\n';
return i;
}
int createAxes(int i){
// X axis
vertices[i++] = vec4( 2.0, 0.0, 0.0, 1.0);
vertices[i++] = vec4(-2.0, 0.0, 0.0, 1.0);
// Y axis
vertices[i++] = vec4( 0.0, 2.0, 0.0, 1.0);
vertices[i++] = vec4( 0.0,-2.0, 0.0, 1.0);
// Z axis
vertices[i++] = vec4( 0.0, 0.0, 2.0, 1.0);
vertices[i++] = vec4( 0.0, 0.0,-2.0, 1.0);
std::cout << i << '\n';
return i;
}
// Initialize
void initialize(){
// generate vertex data
int i = 0;
i = createCube(i);
i = createAxes(i);
if(i != numberOfVertices){
std::cout << "Error creating vertex data: check vertex count\n";
std::exit(0);
}
// set
initCamera();
// load shader and activate shader
GLuint refVertexShader = Angel::InitShader("Vertex_Shader.glsl", "Fragment_Shader.glsl");
glUseProgram(refVertexShader);
// create and activate a new vertex array object (vao)
glGenVertexArrays(1, &refVertexArray);
glBindVertexArray(refVertexArray);
// create and activate a new buffer array object in the vao
glGenBuffers(1, &refVertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, refVertexBuffer);
// load vertex data into the buffer array
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
// load postion pipeline variable
GLuint refVec4Position = glGetAttribLocation(refVertexShader, "Position");
glEnableVertexAttribArray(refVec4Position);
glVertexAttribPointer(refVec4Position, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
// get pointers for uniform variables in shader program
refUniformModelxView = glGetUniformLocation(refVertexShader, "ModelxView");
refUniformProjection = glGetUniformLocation(refVertexShader, "Projection");
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LESS);
glClearColor(0.0, 0.0, 0.0, 1.0);
}
int main(int argc, char* argv[]){
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowSize(S_WIDTH, S_HEIGHT );
glutCreateWindow("TeapotViewer");
glewInit();
initialize();
glutDisplayFunc(draw);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyHandle);
glutMainLoop();
return 0;
}
vertex shader
#version 150
uniform mat4 ModelxView;
uniform mat4 Projection;
in vec4 Position;
void main()
{
gl_Position = Projection*ModelxView*Position;
}
fragment shader
#version 150
out vec4 fColor;
void main()
{
fColor = vec4(1.0, 1.0, 0.0, 1.0);
}

Answer 1

Not sure about this, as I'm not sure what's going on in Angel:: behind the scenes, but is it correct to output fColor from your fragment shader? I thought in glsl 150 it expects the special variable gl_FragColor, unless Angel does something specific to mitigate this.
I looked at this for a while but I don't see anything else that would cause a problem. Unfortunately I think if you're really stuck you might have to start writing a simpler example (no functions, just a straight rundown of initialization through rendering of a triangle).
Also make sure glGetError is called at least once per draw() loop to make sure it's not missing anything. Does Angel throw an exception on link/compilation failure?

Answer 2

Hmm, how about this:
viewMatrix = lookAt(cameraDirection, cameraPosition, cameraUp);
Is this the same lookAt as gluLookAt? In that function the prototype is (position, lookAtPoint, cameraUp), which is backwards of what you've got.