Opengl transparent parts get rendered black

Question

i want too render a texture that has transparent parts on my screen with OpenGL, but the transparent parts appear black for some reason.

Texture:

Screenshot:

The code is:

#define STB_IMAGE_IMPLEMENTATION
#include 
#include "stdlib.h"
#include "GLFW/glfw3.h"
#include "GL/gl.h"
#include "stb_image.h"

int windowheight;
int windowwidth;

void camera();
void program();

void rendertex(int x, int y, int w, int h)
{
    glColor4d(255,255,255,255);
    glDisable(GL_COLOR_MATERIAL);
    glEnable(GL_TEXTURE_2D);
    glShadeModel(GL_SMOOTH);
    int width,height,channel;
    auto *data = stbi_load("../textures/isaac.png",&width,&height,&channel,0);
    GLuint texture;
    glGenTextures(1,&texture);
    glBindTexture(GL_TEXTURE_2D,texture);;
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA, width,height,0,GL_RGBA,GL_UNSIGNED_BYTE,data);

    stbi_image_free(data);

    printf("%d
",width);
    printf("%d
",height);
    printf("%d
",channel);

    glBegin(GL_QUADS);
    glTexCoord2d(0,0);
    glVertex2d(x,y);
    glTexCoord2d(0,1);
    glVertex2d(x,y + h);
    glTexCoord2d(1,1);
    glVertex2d(x + w, y + h);
    glTexCoord2d(1,0);
    glVertex2d(x + w, y);
    glEnd();

    glDisable(GL_TEXTURE_2D);
}
static void key(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    switch (key)
    {
        case GLFW_KEY_ESCAPE:
            exit(0);
        case GLFW_KEY_UP:
            break;
    }
}

int main()
{
    glfwInit();
    GLFWwindow* window = glfwCreateWindow(800,800,"t", nullptr, nullptr);
    glfwMakeContextCurrent(window);
    glfwSetKeyCallback(window,key);
    glfwSwapInterval(1);
    glfwGetFramebufferSize(window,&windowwidth,&windowheight);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    while (!glfwWindowShouldClose(window))
    {
        glfwSwapBuffers(window);
        glfwGetFramebufferSize(window,&windowwidth,&windowheight);
        program();
        camera();
        glfwPollEvents();
    }
}

void program()
{
    glClearColor(255,255,255,255);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_LINES);
    glColor4d(255,0,0,0);
    glVertex2d(0,0);
    glVertex2d(windowwidth,windowheight);
    glEnd();
    glFlush();


    rendertex(20,20,400,500);
}

void camera()
{
    glViewport(0,0,windowwidth,windowheight);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0,windowwidth,windowheight,0,0,1);
    glMatrixMode(GL_MODELVIEW);
}

I already tried commenting some lines out, but no luck. im using linux, if that matters

EDIT: cmakelist.txt

cmake_minimum_required(VERSION 3.15)
project(t)

set(CMAKE_CXX_STANDARD 17)

add_executable(t main.cpp)

target_link_libraries(t GL glfw)

user_5577765 · Answer

You`ve to enable Blending. At blending the color of a fragment is mixed with the current color of the framebuffer, before it is written to the framebuffer.
How the colors are mixed depends on a formula, which can be configured.

Enable blending and specify that the colors are mixed dependent on the color channel of the fragment color:

glEnable(GL_BLEND); 
glBlendEquation(GL_FUNC_ADD); // this is default
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

Note the above code species the following blend function (D means the framebuffer color and C the fragment color):

D_rgba = C_rgba * C_alpha - D_rgba * (1 - C_alpha)

Opengl transparent parts get rendered black

1 Answers