OpenGL program to draw a triangle gives a yellow screen - c++

Question

I am trying to draw a triangle with OpenGL.
My code compiles fine, and does not produce any errors but it still does not do what its supposed to.
I have a vertex shader and a fragment shader and both of them are in the same program.
My code is below:
#include "../../include/sb7.h"
GLuint compile_shaders(void)
{
GLuint vertex_shader;
GLuint fragment_shader;
GLuint program;
// Source code for Vertex Shader
static const GLchar * vertex_shader_source[] =
{
"#version 450 core \n"
" \n"
"void main(void) \n"
"{ \n"
" //Decalre a hardcoded array of positions \n"
" const vec4 vertices[3] = vec4[3](vec4(0.25, -0.25, 0.5, 1.0), \n"
" vec4(-0.25, -0.25, 0.5, 1.0), \n"
" vec4(0.25, 0.25, 0.5, 1.0)); \n"
" //Index into our array using gl_VertexID \n"
" gl_Position = vertices[gl_VertexID]; \n"
"} \n"
};
// Source code for Fragment Shader
static const GLchar * fragment_shader_source[] =
{
"#version 450 core \n"
" \n"
"out vec4 color; \n"
" \n"
"void main(void) \n"
"{ \n"
" color = vec4(0.0, 0.8, 1.0, 1.0); \n"
"} \n"
};
// Create and compiler Vertex Shader
vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, vertex_shader_source, NULL);
glCompileShader(vertex_shader);
// Create and compiler Fragment Shader
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, fragment_shader_source, NULL);
glCompileShader(fragment_shader);
// Create program, attach shaders to it, and link it
program = glCreateProgram();
glAttachShader(program, vertex_shader);
glAttachShader(program, fragment_shader);
glLinkProgram(program);
// Delete shaders as program has them now
glDeleteShader(vertex_shader);
glDeleteShader(fragment_shader);
return program;
};
class my_application : public sb7::application
{
public:
void startup()
{
rendering_program = compile_shaders();
glCreateVertexArrays(1, &vertex_array_object);
glBindVertexArray(vertex_array_object);
}
void shutdown()
{
glDeleteVertexArrays(1, &vertex_array_object);
glDeleteProgram(rendering_program);
glDeleteVertexArrays(1, &vertex_array_object);
}
// Our rendering function
void render(double currentTime)
{
// Sets Colour
static const GLfloat color[] = { 0.0f, 0.2f, 0.0f, 1.0f };
glClearBufferfv(GL_COLOR, 0, color);
// Use program object we created for rendering
glUseProgram(rendering_program);
// Draw one triangle
glDrawArrays(GL_TRIANGLES, 0, 3);
}
private:
GLuint rendering_program;
GLuint vertex_array_object;
};
I am following the OpenGL Superbible, 7th edition.
The same program (with small changes) was also not drawing a point even when I changed the point size and the output was the same screen (full yellow) that I am getting for this.
I have seen similar problems that arise during drawing of triangles but they are all different from what I'm doing.
How do I fix this?

Answer 1

Workin' fine here:
All together:
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <cstdarg>
#include <cstdlib>
struct Program
{
static GLuint Load( const char* shader, ... )
{
GLuint prog = glCreateProgram();
va_list args;
va_start( args, shader );
while( shader )
{
const GLenum type = va_arg( args, GLenum );
AttachShader( prog, type, shader );
shader = va_arg( args, const char* );
}
va_end( args );
glLinkProgram( prog );
CheckStatus( prog );
return prog;
}
private:
static void CheckStatus( GLuint obj )
{
GLint status = GL_FALSE;
if( glIsShader(obj) ) glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
if( glIsProgram(obj) ) glGetProgramiv( obj, GL_LINK_STATUS, &status );
if( status == GL_TRUE ) return;
GLchar log[ 1 << 15 ] = { 0 };
if( glIsShader(obj) ) glGetShaderInfoLog( obj, sizeof(log), NULL, log );
if( glIsProgram(obj) ) glGetProgramInfoLog( obj, sizeof(log), NULL, log );
std::cerr << log << std::endl;
exit( EXIT_FAILURE );
}
static void AttachShader( GLuint program, GLenum type, const char* src )
{
GLuint shader = glCreateShader( type );
glShaderSource( shader, 1, &src, NULL );
glCompileShader( shader );
CheckStatus( shader );
glAttachShader( program, shader );
glDeleteShader( shader );
}
};
const char* vert = R"GLSL(
#version 450 core
void main(void)
{
//Decalre a hardcoded array of positions
const vec4 vertices[3] = vec4[3]
(
vec4(0.25, -0.25, 0.5, 1.0),
vec4(-0.25, -0.25, 0.5, 1.0),
vec4(0.25, 0.25, 0.5, 1.0)
);
//Index into our array using gl_VertexID
gl_Position = vertices[gl_VertexID];
}
)GLSL";
const char* frag = R"GLSL(
#version 450 core
out vec4 color;
void main(void)
{
color = vec4(0.0, 0.8, 1.0, 1.0);
}
)GLSL";
int main( int argc, char** argv )
{
glfwInit();
glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 4 );
glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 5 );
glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
glfwWindowHint( GLFW_OPENGL_DEBUG_CONTEXT, GL_TRUE );
GLFWwindow* window = glfwCreateWindow( 640, 480, "51307782", NULL, NULL );
glfwMakeContextCurrent( window );
glewInit();
glfwSwapInterval( 1 );
GLuint rendering_program = Program::Load
(
vert, GL_VERTEX_SHADER,
frag, GL_FRAGMENT_SHADER,
NULL
);
GLuint vertex_array_object = 0;
glCreateVertexArrays( 1, &vertex_array_object );
glBindVertexArray( vertex_array_object );
while( !glfwWindowShouldClose( window ) )
{
glfwPollEvents();
static const GLfloat color[] = { 0.0f, 0.2f, 0.0f, 1.0f };
glClearBufferfv( GL_COLOR, 0, color );
glUseProgram( rendering_program );
glDrawArrays( GL_TRIANGLES, 0, 3 );
glfwSwapBuffers( window );
}
glDeleteVertexArrays( 1, &vertex_array_object );
glDeleteProgram( rendering_program );
glfwDestroyWindow( window );
glfwTerminate();
}