Why is the sprite not rendering in OpenGL? - c++

Question

I am trying to render a 2D(Screen coordinated) sprite in OpenGL. Yet, when I compile it, it does not show up. I see that the code is fine (There are not even any shader compilation errors nor any other errors). I also have also the matrices set up(which I doubt is causing the problem, and that's where starts the CONFUSION!!)
Here is the source code, by the way(without debugging, to make it short):-
main.cpp
// Including all required headers here...
#include <iostream>
#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include "SOIL2/SOIL2.h"
#include <glm/glm.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <glm/gtc/matrix_transform.hpp>
const GLchar * vertexShaderSource =
"#version 330 core\n"
"layout(location = 0) in vec4 vertex;\n"
"out vec2 TexCoords;\n"
"uniform mat4 model;\n"
"uniform mat4 projection;\n"
"void main()\n"
"{\n"
"TexCoords = vertex.zw;\n"
"gl_Position = projection * model * vec4(vertex.xy, 0.0, 1.0);\n"
"}\0";
const GLchar * fragmentShaderSource =
"#version 330 core\n"
"in vec2 TexCoords;\n"
"out vec4 color;\n"
"uniform sampler2D image;\n"
"uniform vec3 spriteColor;\n"
"void main()\n"
"{\n"
"color = vec4(spriteColor, 1.0) * texture(image, TexCoords);\n"
"}\0";
const GLint WIDTH = 800, HEIGHT = 600;
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_FALSE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow *window = glfwCreateWindow(WIDTH, HEIGHT, "Rendering Sprites", nullptr, nullptr);
int screenWidth, screenHeight;
glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
glewInit();
glViewport(0, 0, screenWidth, screenHeight);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
glCompileShader(vertexShader);
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, NULL);
glCompileShader(fragmentShader);
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
GLuint quadVAO;
GLuint VBO;
GLfloat vertices[] =
{
0.0f, 1.0f, 0.0f, 1.0f,
1.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 1.0f,
1.0f, 1.0f, 1.0f, 1.0f,
1.0f, 0.0f, 1.0f, 0.0f
};
glGenVertexArrays(1, &quadVAO);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindVertexArray(quadVAO);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (GLvoid*)0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
GLuint texture;
int width, height;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
unsigned char *image = SOIL_load_image("img.png", &width, &height, 0, SOIL_LOAD_RGBA);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
SOIL_free_image_data(image);
glBindTexture(GL_TEXTURE_2D, 0);
while (!glfwWindowShouldClose(window))
{
glfwPollEvents();
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
glm::mat4 model;
glm::mat4 projection = glm::ortho(0.0f, static_cast<GLfloat>(WIDTH), static_cast<GLfloat>(HEIGHT), 0.0f, -1.0f, 1.0f);
glm::vec2 size = glm::vec2(10.0f, 10.0f);
glm::vec2 position = glm::vec2(-10.0f, 10.0f);
glm::vec3 color = glm::vec3(1.0f, 0.0f, 0.0f);
GLfloat rotation = 0.0f;
model = glm::translate(model, glm::vec3(position, 0.0f));
model = glm::translate(model, glm::vec3(0.5f * size.x, 0.5f * size.y, 0.0f));
model = glm::rotate(model, rotation, glm::vec3(0.0f, 0.0f, 1.0f));
model = glm::translate(model, glm::vec3(-0.5f * size.x, -0.5f * size.y, 0.0f));
model = glm::scale(model, glm::vec3(size, 1.0f));
glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
glUniformMatrix4fv(glGetUniformLocation(shaderProgram, "model"), 1, GL_FALSE, glm::value_ptr(model));
glUniform3f(glGetUniformLocation(shaderProgram, "spriteColor"), color.x, color.y, color.z);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);
glBindVertexArray(quadVAO);
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindVertexArray(0);
glfwSwapBuffers(window);
}
glDeleteVertexArrays(1, &quadVAO);
glDeleteBuffers(1, &VBO);
glfwTerminate();
return EXIT_SUCCESS;
}

Answer 1

You have to initialize the model matrix variable glm::mat4 model.
The glm API documentation refers to The OpenGL Shading Language specification 4.20.
5.4.2 Vector and Matrix Constructors
If there is a single scalar parameter to a vector constructor, it is used to initialize all components of the constructed vector to that scalar’s value. If there is a single scalar parameter to a matrix constructor, it is used to initialize all the components on the matrix’s diagonal, with the remaining components initialized to 0.0.
This means, that an identity matrix can be initialized by the single parameter 1.0:
glm::mat4 model(1.0f);
Further your sprite is very small and it is out of the viewport (clip space) at the left side:
Change your code like this:
glm::vec2 position = glm::vec2(10.0f, 10.0f); // 10.0f instead of -10.0f