OpenGL Light blending

[LucdoOf]

Hello there,

I’m trying to do a light mask with OpenGL.
I have a texture rendered in the background, i have light sources and i have a fragment shader generating light halo around given light.

What i can do actually:
I can render a halo of the light color around lights separately from the background texture

What i’m trying to do:
I want that the background image take the color of my light (not sure if this is very clear but i don’t want my light to be above the background, i want my light to change the background color)

I attempted to use blend equations to do that,
Here is my actual code:

private void render() {
    glClear(GL_COLOR_BUFFER_BIT);
    glBlendFunc(GL_ONE, GL_ONE);

    Texture.TEXTURE.bind();
    glBegin(GL_QUADS);
        glColor4f(1f, 1f, 1f, 1);
        glTexCoord2d(0, 0); glVertex2f(0, 0);
        glTexCoord2d(1, 0); glVertex2f(width, 0);
	    glTexCoord2d(1, 1); glVertex2f(width, height);
	    glTexCoord2d(0, 1); glVertex2f(0, height);
	glEnd();
	Texture.TEXTURE.unbind();

    glBlendFunc(GL_ZERO, GL_SRC_ALPHA); 

    for (Light light : lights) {
        glUseProgram(shaderProgram);
	    glUniform2f(glGetUniformLocation(shaderProgram, "lightLocation"), light.location.getX(), height - light.location.getY());
	    glUniform3f(glGetUniformLocation(shaderProgram, "lightColor"), light.red, light.green, light.blue);

		glBegin(GL_QUADS); {
			glVertex2f(0, 0);
			glVertex2f(0, height);
			glVertex2f(width, height);
			glVertex2f(width, 0);
		} glEnd();

		glUseProgram(0);
    }}

According to the andersriggelsen simulator (can’t put the link here), with the given parameters of blGlendFunc and with a gradiant background the result looks just like what i’m trying to do but my screen is black using this code…

Also: testing with the gradiant from the andersriggelsen simulator on my project does work like a charm (and yes my fragment shader is correct, without the blend it generate a perfect light halo)

Thanks you in advance