glDrawArrays is not working for some reason? - c++

Question

I do not understand why this is not working with glDrawArrays.
If you see anything out of place or missing I really need to know.
#define GLEW_STATIC
#include <GL/glew.h>
static int CompileShader(unsigned int type, const std::string& Source) {
unsigned int id = glCreateShader(type);
const char* src = Source.c_str();
glShaderSource(id, 1, &src, nullptr);
glCompileShader(id);
int result;
glGetShaderiv(id, GL_COMPILE_STATUS, &result);
if (result == GL_FALSE) {
int length;
glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
char* message = (char*)alloca(length * sizeof(char));
glGetShaderInfoLog(id, length, &length, message);
std::cout << message ;
}
return id;
}
static unsigned int CreateShader(const std::string& Vertexshader, const std::string& Fragmentshader) {
unsigned int program = glCreateProgram();
unsigned int vertex = CompileShader(GL_VERTEX_SHADER, Vertexshader);
unsigned int fragment = CompileShader(GL_FRAGMENT_SHADER, Fragmentshader);
glAttachShader(program, vertex);
glAttachShader(program, fragment);
glLinkProgram(program);
glValidateProgram(program);
return program;
}
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
if (GLEW_OK == glewInit())
{
}
float vertices[6] = {
-0.5, -0.5,
0.0, 0.5,
0.5, 0.5
};
unsigned int buffer1;
glGenBuffers(1, &buffer1);
glBindBuffer(GL_ARRAY_BUFFER, buffer1);
glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 6, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
glEnableVertexAttribArray(0);
std::string Vertexshader =
"#version 330 core\n"
"\n"
"layout (location = 0)in vec4 position;"
"\n"
"void main()\n"
"{\n"
" gl_Position = position;\n"
"}\n";
std::string Fragmentshader =
"#version 330 core\n"
"\n"
"layout (location = 0)out vec4 color;"
"\n"
"void main()\n"
"{\n"
" color = vec4(1.0, 0.0, 0.0, 1.0);\n"
"}\n";
unsigned int shader = CreateShader(Vertexshader, Fragmentshader);
glUseProgram(shader);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shader);
glDrawArrays(GL_TRIANGLES, 0, 3);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}

Answer 1

The 2nd parameter of glVertexAttribPointer is the tuple size of a coordinate, rather then the number of floats in the array of vertices.
Each of the vertices in the array consists of 2 components, hence the size argument has to be 2 rather than 6:
glVertexAttribPointer(0, 6, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);