OpenGL camera movement program vertex shader issue - c++

Question

So, I'm a beginner learning graphics programmer. I'm working on a program for camera movement. I think there's something wrong with the vertex shader. The program runs with no errors but the screen is completely blank. Here is the vertex shader I'm using:
#version 330
in vec4 vPosition;
out vec4 vColor;
uniform mat4 model_view;
uniform mat4 projection;
void main()
{
vec4 pos = projection * model_view * vPosition / vPosition.w;
gl_Position = pos;
vColor = vPosition;
}
If I switch the shader back to basic version:
#version 330
in vec4 vPosition;
out vec4 vColor;
void
main()
{
gl_Position = vPosition;
vColor = vPosition;
}
The program runs and renders a triangle successfully. So, I'm pretty sure the error is with the shader.
The shader is called in the initialize function:
void initialize(void)
{
glClearColor(1.0, 1.0, 1.0, 1.0); // white background
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
// Create and initialize a buffer object
GLuint buffer;
glGenBuffers(1, &buffer);
glBindBuffer(GL_ARRAY_BUFFER, buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);
// Load shaders and use the resulting shader program
GLuint program = InitShader("res/shaders/vshader21.glsl", "res/shaders/fshader21.glsl");
model_view = glGetUniformLocation(program, "model_view");
projection = glGetUniformLocation(program, "projection");
glUseProgram(program);
// Initialize the vertex position attribute from the vertex shader
GLuint loc = glGetAttribLocation(program, "vPosition");
glEnableVertexAttribArray(loc);
glVertexAttribPointer(loc, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
}
the 'points' in glBufferData is as follows:
const int WIDTH = 500, HEIGHT = 500;
/* Positions */
vec4 points[] = {
vec4(0.5,0.5, 1, 1),
vec4(-0.5,0.5, 1, 1),
vec4(0.5,-0.5, 1, 1) ,
vec4(-0.5,-0.5, 1, 1)
};
model_view and projection are of GLuint type in main application and global.
I set the uniform variables (position, model_view) in the display functions.
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT); // clear the window
glPointSize(20.0);
// Projection transformation parameters
GLfloat left = -1.0, right = 1.0;
GLfloat bottom = -1.0, top = 1.0;
GLfloat zNear = 0, zFar = 3.0;
mat4 p = Ortho(left, right, bottom, top, zNear, zFar);
glUniformMatrix4fv(projection, 1, GL_TRUE, p);
vec4 eye(0.0, 0.0, -1.0, 1.0);
vec4 at(0.0, 0.0, 0.0, 1.0);
vec4 up(0.0, 1.0, 0.0, 0.0);
mat4 mv = LookAt(eye, at, up);
glUniformMatrix4fv(model_view, 1, GL_TRUE, mv);
glDrawArrays(GL_TRIANGLES, 0, 3); // draw the points
glFlush();
}
What could possibly be going wrong?

Answer 1

The explicit division by the .w component is superfluous.
vec4 pos = projection * model_view * vPosition / vPosition.w;
vec4 pos = projection * model_view * vPosition;
Note, the Perspective divide is automatically performed after clipping.
Since the vector is multiplied to the uniforms form the right, you do not have to transpose the matrices:
glUniformMatrix4fv(projection, 1, GL_TRUE, p);
glUniformMatrix4fv(projection, 1, GL_FALSE, p);
glUniformMatrix4fv(model_view, 1, GL_TRUE, mv);
glUniformMatrix4fv(model_view, 1, GL_FALSE, mv);
See GLSL Programming/Vector and Matrix Operations