Hi people. I started to study opengl through a tutorial and I have a need of rendering a semi-transparent triangle using shaders. I was able to draw a triangle, but as soon as I add blending, no matter the color, the triangle doesn’t get drawn anymore.
I wrote an example of the issue:
#include <glad/glad.h>
#include <GLFW/glfw3.h>
auto constexpr WIDTH = 800;
auto constexpr HEIGHT = 600;
auto constexpr TITLE = "Draft 4";
const char* vertexShaderSource = "#version 330 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
" gl_Position = vec4(aPos, 1.0);\n"
"}\0";
const char* fragmentShaderSource = "#version 330 core\n"
"out vec4 FragColor;\n"
"uniform vec4 color;\n"
"void main()\n"
"{\n"
" FragColor = color;\n"
"}\0";
void window_size_callback(GLFWwindow* window, int width, int height)
{
glViewport(0, 0, width, height);
}
int main(int argc, char* argv[])
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
auto window = glfwCreateWindow(WIDTH, HEIGHT, TITLE, nullptr, nullptr);
glfwSetWindowSizeCallback(window, window_size_callback);
glfwMakeContextCurrent(window);
glfwSwapInterval(1);
gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
// if the following two lines are present, the triangle isn't drawn at al
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertexShader, 1, &vertexShaderSource, nullptr);
glCompileShader(vertexShader);
// TODO: check for shader compilation errors
unsigned int fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragmentShader, 1, &fragmentShaderSource, nullptr);
glCompileShader(fragmentShader);
// TODO: check for shader compilation errors
unsigned int shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// TODO: check for shader linking errors
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
unsigned int VBO, VAO;
float vertices[] = {
-0.5, -0.5, 0.0f,
0.5, -0.5, 0.0f,
0.0, 0.5, 0.0f
};
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*) 0);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
int vertexColorLocation = glGetUniformLocation(shaderProgram, "color");
glUniform4f(vertexColorLocation, 0.0, 0.0, 0.0, 1.0);
bool running = true;
while (running) {
glfwPollEvents();
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(shaderProgram);
glBindVertexArray(VAO);
glDrawArrays(GL_TRIANGLES, 0, 3);
glfwSwapBuffers(window);
if(glfwWindowShouldClose(window)){
running = false;
}
}
glDeleteProgram(shaderProgram);
glfwSetWindowSizeCallback(window, nullptr);
glfwWindowShouldClose(window);
glfwTerminate();
return 0;
}
Can you help me to spot the mistake? Thank you.