I am going to start a tutorial series on how to make GLSL ES shaders for GameMaker: Studio
What a shader is
the vertex shader and the fragment (or pixel) shader. Shaders are used in games and software as effects to distort or recolor graphics. Shaders can be used for anything from grayscale effects to ripples to lighting engines and much more.
What you'll need to know
You will also want to know how to code in GML (GameMaker's programming language).
vec3 Vector = vec3( 0.0, 1.0, 2.0) ;
The vec3 at the beginning tells what kind of vector or float the variable is. The second vec3 is for setting each of the values to their corresponding positions. So basically a vec4 has the components R, G, B, and A (Red, green, blue and alpha). When you set it to vec4( 0.0, 0.5, 0.8, 1.0) the R component of the vector is set to 0.0 while the G part is set to 0.5. decimals are added to all whole numbers in shaders to avoid errors. With this knowledge we are able to set certain parts of vector like this:
vec4 Vector = vec4( 0.0, 1.0, 2.0, 3.0);
Vector.rb = vec2( 4.0, 5.0);//Doesn't need to be redefined
The second time we set "Vector", we only set the R and B components. This way we are able to specify what we're setting.
"gl_FragColor" is a 4 dimensional vector (vec4). What ever you set gl_FragColor to is the output of the pixel (does this for each pixel). The reason it is a vec4 is because it outputs a combination of red, green, and blue (the primary colors of light) to form the output color and alpha. The alpha (transparency) is used in GameMaker to tell how much of underlying colors to show.
if we set gl_FragColor to vec4( 1.0, 0.0, 0.0, 1.0) it would mean the R component (Red) and the A components (Alpha) are set to 1.0. In shaders, red set to 1 means fully red (rather than whole the number range being from 0 to 255). So this code would output a fully red block for each pixel. Since that shader wouldn't be very useful, we will try something else. I'll explain in more detail in a later post. Shaders in GameMaker: Studio must be applied to something drawn. So a shader could be applied to a sprite, background, or anything else you can draw. The "texture2D()" function outputs the color of the texture (the thing the shader is applied to) at each pixel. We will discuss this in detail in a later tutorial. For now just know that "gl_FragColor = v_vColour * texture2D( gm_BaseTexture, v_vTexcoord )" means that it draws the texture like normal. If we try this code it will make the colors much more intense:
varying vec2 v_vTexcoord;
varying vec4 v_vColour;
gl_FragColor = v_vColour * texture2D( gm_BaseTexture, v_vTexcoord );
gl_FragColor.rgb *= vec3(2.0,2.0,2.0);//this doubles the red, green and blue values
So what this does is it sets the color to the texture color and then doubles the red, green and blue colors.
Shaders and Gamemaker
draw_background(background,0,0)//any draw code should work
Create a room, place the object in it and then test the game.
You should see the color intensified properly.
Next is the BLACK AND WHITE SHADER tutorial.