Different fragment shader colors - c++

Question

I want to draw different figures with different colors using shaders.
I tried using uniform variables and using vertex attributes of the meshes to separate Vertex Buffer Objects but when I run the program only the second color is used and the first figure isn't shown at all. Im not sure if it's an issue with how I bind the shaders or with the way I use uniform variables. Thanks in advance.
Here is the code:
#include <GL/glew.h>
#include <GL/glut.h>
#include <stdio.h>
const char* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\0";
const char* fragmentShaderSource = "#version 330 core\n"
"in vec4 color;\n"
"out vec4 FragColor;\n"
"uniform vec3 figColor;\n"
"void main()\n"
"{\n"
" FragColor = vec4(figColor, 0.0f);\n"
"}\n\0";
// Set of vertices that draw the different figures:
float vertices1[] = {
-0.8f, 0.6f, 0.0f,
-0.8f, 0.4f, 0.0f,
-0.83f, 0.44f, 0.0f,
-0.87f, 0.51f, 0.0f,
-0.9f, 0.57f, 0.0f,
-0.93f, 0.63f, 0.0f,
-0.95f, 0.69f, 0.0f,
-0.97f, 0.75f, 0.0f,
-0.98f, 0.8f, 0.0f,
-0.91f, 0.8f, 0.0f,
-0.85f, 0.79f, 0.0f,
-0.8f, 0.77f, 0.0f,
};
float vertices2[] = {
-0.8f, -0.15f, 0.0f,
-1.0f, 0.0f, 0.0f,
-0.95f, 0.0f, 0.0f,
-0.86f, -0.01f, 0.0f,
-0.81f, -0.02f, 0.0f,
-0.75f, -0.03f, 0.0f,
};
GLuint vertexShader;
GLuint fragmentShader;
GLuint shaderProgram;
void display(void) {
// Background color.
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
GLint uniform = glGetUniformLocation(shaderProgram, "figColor");
glUniform3f(uniform, 1.0f, 0.0f, 0.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, 12);
glUniform3f(uniform, 0.0f, 0.749f, 1.0f);
glDrawArrays(GL_TRIANGLE_FAN, 0, 6);
glUseProgram(0);
glFlush();
}
// Main.
int main(int argc, char** argv) {
glutInit(&argc, argv);
// Color mode.
glutInitDisplayMode(GLUT_RGBA);
// Window size.
glutInitWindowSize(500, 500);
// Title.
glutCreateWindow("Tarea 3: Figura con curvas");
GLenum err = glewInit();
if (err != GLEW_OK) {
printf("glewInit failed: %s", glewGetErrorString(err));
exit(1);
}
// Compile vertex shader.
vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
// Check for vertex shader compilation errors.
int success;
char infoLog[512];
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (!success) {
glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
printf("ERROR::SHADER::VERTEX::COMPILATION_FAILED\n");
}
// Compile fragment shader.
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
// Check for fragment shader compile errors.
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (!success) {
glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
printf("ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n");
}
// Link and delete shaders.
shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
//Separating the Vertex Buffer Objects.
GLuint VBOs[2];
glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);
// Specify a VertexArrayObject for each mesh.
GLuint VAOs[2];
glGenVertexArrays(2, VAOs);
glBindVertexArray(VAOs[0]);
glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
glBindVertexArray(VAOs[1]);
glBindBuffer(GL_ARRAY_BUFFER, VBOs[1]);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// Bind the VAO before the draw call.
glBindVertexArray(VAOs[0]);
glDrawArrays(GL_TRIANGLE_FAN, 0, 12);
glBindVertexArray(VAOs[1]);
glDrawArrays(GL_TRIANGLE_FAN, 0, 24);
// Displaying the figures.
glutDisplayFunc(display);
glutMainLoop();
}

Answer 1

You missed to generate the vertex buffer object names:
//Separating the Vertex Buffer Objects.
GLuint VBOs[2];
glGenBuffers(2, VBOs); <----
You have to bind the vertex array before drawing the mesh in the main loop:
GLuint VAOs[2];
void display(void) {
// Background color.
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
GLint uniform = glGetUniformLocation(shaderProgram, "figColor");
glUniform3f(uniform, 1.0f, 0.0f, 0.0f);
glBindVertexArray(VAOs[0]); // <---
glDrawArrays(GL_TRIANGLE_FAN, 0, 12);
glUniform3f(uniform, 0.0f, 0.749f, 1.0f);
glBindVertexArray(VAOs[1]); // <----
glDrawArrays(GL_TRIANGLE_FAN, 0, 6);
glUseProgram(0);
glFlush();
}
int main(int argc, char** argv) {
// [...]
// Specify a VertexArrayObject for each mesh.
// GLuint VAOs[2]; <---- DELETE
glGenVertexArrays(2, VAOs);
// [...]
// DELETE
/*
// Bind the VAO before the draw call.
glBindVertexArray(VAOs[0]);
glDrawArrays(GL_TRIANGLE_FAN, 0, 12);
glBindVertexArray(VAOs[1]);
glDrawArrays(GL_TRIANGLE_FAN, 0, 24);
*/
// [...]