Opengl two different triangles with two shader programs - c++

Question

I want to create 2 triangles with different colors that they change to wireframe mode when I press "Tab" my problem is that I have two VBO and two shaders programs but it only compile one triangle
#include <GL\glew.h>
#include <GLFW\glfw3.h>
#include <iostream>
bool flag;
void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);
const char* vertex_shader =
"#version 110 \n"
"attribute vec3 in_position; \n"
"void main() \n"
"{ \n"
" gl_Position = vec4(in_position.x, in_position.y, in_position.z, 1.0);\n"
"} \n";
const char* fragment_shader =
"#version 110 \n"
"void main (void) \n"
"{ \n"
" gl_FragColor = vec4(0.7,0.3,0.3, 1.0); \n"
"} \n";
const char* vertex_shader1 =
"#version 110 \n"
"attribute vec3 in_position; \n"
"void main() \n"
"{ \n"
" gl_Position1 = vec4(in_position.x, in_position.y, in_position.z, 1.0);\n"
"} \n";
const char* fragment_shader1 =
"#version 110 \n"
"void main (void) \n"
"{ \n"
" gl_FragColor1 = vec4(0.4,0.7,0.3, 1.0); \n"
"} \n";
int main()
{
//Initialize GLFW
if (!glfwInit()) //if GLFW is not initialized correctly, exit
{
std::cout << "Failed to initialize GLFW" << std::endl;
return -1;
}
//Create the window
GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", NULL, NULL);
if (window == NULL) //if the window was not created correctly, exit
{
std::cout << "Failed to create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
//Specify OpenGL version
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
//Make the context that was created the current one
glfwMakeContextCurrent(window);
//Initialize GLEW
if (glewInit() != GLEW_OK) //if GLEW was not initialized correctly, exit
{
std::cout << "Failed to initialize GLEW" << std::endl;
glfwTerminate();
return -1;
}
//Set the viewport size changing function
glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
//Rectangle vertices, to uncomment select the area and press Ctr+K,Ctr+U
float vertices[] =
{
// first triangle
0.55f, 0.5f, 0.0f, // top right
0.55f, -0.5f, 0.0f, // bottom right
-0.45f, 0.5f, 0.0f, // top left
};
float vertices1[] =
{
// second triangle
0.45f, -0.5f, 0.0f, // bottom right
-0.55f, -0.5f, 0.0f, // bottom left
-0.55f, 0.5f, 0.0f // top left
};
//Create the triangle VBO
GLuint triangle_vbo;
glGenBuffers(1, &triangle_vbo); //generate a unique buffer ID
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo); //bind the VBO to the context
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//copy user-defined data into the currently bound buffer
glBindBuffer(GL_ARRAY_BUFFER, 0); //unbind the VBO
//Create a vertex shader object
GLuint vertexShader;
vertexShader = glCreateShader(GL_VERTEX_SHADER); //ID of the shader object
glShaderSource(vertexShader, 1, &vertex_shader, NULL); //attach the shader source code to the shader object
glCompileShader(vertexShader);//compile the shader
//Create a fragment shader object
GLuint fragmentShader;
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragment_shader, NULL);
glCompileShader(fragmentShader);
//Create a shader program object
GLuint shaderProgram;
shaderProgram = glCreateProgram(); //create the program ID
glAttachShader(shaderProgram, vertexShader); //attach the shaders to the program
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram); // link the program
//Delete the vertex andd fragment shader objects
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
//Create the triangle VBO
GLuint triangle_vbo1;
glGenBuffers(1, &triangle_vbo1); //generate a unique buffer ID
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo1); //bind the VBO to the context
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);//copy user-defined data into the currently bound buffer
glBindBuffer(GL_ARRAY_BUFFER, 0); //unbind the VBO
//Create a vertex shader object
GLuint vertexShader1;
vertexShader1 = glCreateShader(GL_VERTEX_SHADER); //ID of the shader object
glShaderSource(vertexShader1, 1, &vertex_shader1, NULL); //attach the shader source code to the shader object
glCompileShader(vertexShader1);//compile the shader
//Create a fragment shader object
GLuint fragmentShader1;
fragmentShader1 = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader1, 1, &fragment_shader1, NULL);
glCompileShader(fragmentShader1);
//Create a shader program object
GLuint shaderProgram1;
shaderProgram1 = glCreateProgram(); //create the program ID
glAttachShader(shaderProgram1, vertexShader1); //attach the shaders to the program
glAttachShader(shaderProgram1, fragmentShader1);
glLinkProgram(shaderProgram1); // link the program
//Delete the vertex andd fragment shader objects
glDeleteShader(vertexShader1);
glDeleteShader(fragmentShader1);
//Rendering loop
while(!glfwWindowShouldClose(window))
{
//Process input
processInput(window);
//Clear the buffers
glClearColor(1.0f, 1.0f, 1.0f, 1.0f); //dark green
//glClearColor(0.5f, 0.0f, 0.0f, 1.0f); //maroon
glClear(GL_COLOR_BUFFER_BIT);
if(flag==true)
{
glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
}
else glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
//Render objects...
glUseProgram(shaderProgram); //use a shader program
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo); //bind the VBO
//tell OpenGL how to read and assign the VBO to the attribute
GLint in_pos = glGetAttribLocation(shaderProgram, "in_position");
glVertexAttribPointer(in_pos, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GL_FLOAT), (void*)0);
glEnableVertexAttribArray(in_pos);
glUseProgram(shaderProgram);
glUseProgram(shaderProgram1);
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo1);
GLint in_pos1 = glGetAttribLocation(shaderProgram1, "in_position");
glVertexAttribPointer(in_pos1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GL_FLOAT), (void*)0);
glEnableVertexAttribArray(in_pos1);
glDrawArrays(GL_TRIANGLES, 0, 6); //draw the triangle
//Swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
glfwSwapBuffers(window);
glfwPollEvents();
}
//Terminate GLFW before exit
glfwTerminate();
return 0;
}
//Viewport size changing function
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
glViewport(0, 0, width, height);
}
//Input
void processInput(GLFWwindow *window)
{
if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
glfwSetWindowShouldClose(window, true);
if(glfwGetKey(window, GLFW_KEY_TAB) == GLFW_PRESS)
flag=true;
else flag=false;
}
The Tab switch changes to wireframe mode as I long keep pressing the "Tab". I want to change only with one click and when click again to change to default

Answer 1

The 2nd vertex shader and fragment shader won't compile, because gl_Position1 and gl_FragColor1 are not valid output variables. You have to use gl_Position and gl_FragColor. See Vertex Shader and Fragment Shader
const char* vertex_shader1 =
"#version 110 \n"
"attribute vec3 in_position; \n"
"void main() \n"
"{ \n"
" gl_Position = vec4(in_position.x, in_position.y, in_position.z, 1.0);\n"
"} \n";
const char* fragment_shader1 =
"#version 110 \n"
"void main (void) \n"
"{ \n"
" gl_FragColor = vec4(0.4,0.7,0.3, 1.0); \n"
"} \n";
I recommend to use glGetShaderiv to verify if the shader code was compiled successfully.
e.g.
GLint status;
glGetShaderiv(vertex_shader1, GL_COMPILE_STATUS, &status);
Use glGetProgramiv with the GL_LINK_STATUS parameter to check if the program was linked successfully.
You have 2 vertex buffers with each 3 vertices, so you have to call glDrawArrays(GL_TRIANGLES, 0, 3); twice and not one time glDrawArrays(GL_TRIANGLES, 0, 6);.
Bind the buffer, define and enable the array of generic vertex attribute data and then draw the triangle:
glUseProgram(shaderProgram);
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo); //bind the VBO
GLint in_pos = glGetAttribLocation(shaderProgram, "in_position");
glVertexAttribPointer(in_pos, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GL_FLOAT), (void*)0);
glEnableVertexAttribArray(in_pos);
glDrawArrays(GL_TRIANGLES, 0, 3); //draw the 1st triangle
glUseProgram(shaderProgram1);
glBindBuffer(GL_ARRAY_BUFFER, triangle_vbo1);
GLint in_pos1 = glGetAttribLocation(shaderProgram1, "in_position");
glVertexAttribPointer(in_pos1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GL_FLOAT), (void*)0);
glEnableVertexAttribArray(in_pos1);
glDrawArrays(GL_TRIANGLES, 0, 3); //draw the 2nd triangle
See the preview: