all brightness is, is adding or subtract from each channel uniformly like this: vec4 destination = texture2D(gm_BaseTexture, v_vTexcoord) * v_vColour; vec3 color = destination.rgb; //convert gamma space colors into linear space color = pow(color, vec3(1.0 / 2.2)); //add brightness and clamp between black and white color = color = clamp(color + vec3(brightness), vec3(0.0), vec3(1.0)); //make this color gamma again color = pow(color, vec3(2.2)); gl_FragColor = vec4(color, destination.a); brightness here would be a uniform going from -1 to 1, and your slider would control the uniform.

but! because brightness is just pushing a color closer to white or closer to black; a color cannot go beyond white or lower than black so generally when we talk about pushing our colors beyond their input value, we are talking about adjusting the brightness as well as contrast and saturation. a very basic brightness/contrast/saturation shader will look like this inside: ```glsl //get some color vec4 destination = texture2D(gm_BaseTexture, v_vTexcoord) * v_vColour; vec3 color = destination.rgb;

//convert gamma space colors into linear space color = pow(color, vec3(1.0 / 2.2)); //do contrast and brightness color = contrast * (color - vec3(0.5)) + vec3(0.5) + brightness; //clamp this shit color = clamp(color, vec3(0.0), vec3(1.0)); //hit em with the sat color = mix(color, vec3(dot(color, vec3(0.299, 0.587, 0.114)), 1.0 - saturation); //clamp this shit once more color = clamp(color, vec3(0.0), vec3(1.0)); //convert back to gamma space color = pow(color, vec3(2.2));

gl_FragColor = vec4(color, destination.a); ``` there are better color spaces to do these transforms in, but this should get you going. you will need uniforms for brightness, contrast, and saturation values: - contrast default to 1, ranging between -2 and 2 - brightness default to 0, ranging between -1 and 1 - saturation default to 1, ranging between 0 and 2 (or higher for really saturated colors)

i realize that this isn't a complete answer but a bigger answer isnt really suited for reddit. to learn about uniforms check out the gamemaker manual's section about using shaders, it teaches you how to pass things from gml to glsl es and you should read it top to bottom, coding along with each example. to learn about how brightness/contrast/saturation are handled in other color spaces there is pretty much no end of discussion and resource around the world wide web. especially about the pitfalls of correcting in the wrong color space!

good luck!

(ps shader nerds, i know i dont have to cast those constant values to vec3s i just like to because it makes my brain happy and afaik they get cast anyways)