59 lines
2.0 KiB
Markdown
59 lines
2.0 KiB
Markdown
# Materials: Shaders
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Shaders are referring to GPU-oriented pieces of a program, performing shading and rendering related functions instead of letting the engine handle it.
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In **FTEQW** you can specify a custom GLSL or HLSL shader using the [program](Documentation/Materials/commands/program.md) command inside a [Material](Documentation/Materials/MatOverview.md).
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## Example Shader
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This is a primitive shader file. It includes the vertex and fragment program.
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It will respond to the [diffusemap](Documentation/Materials/commands/diffusemap.md) only, which is loaded
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into the **d_f** variable. It can be modified from that point onwards.
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The commented out line will turn all of the output red.
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Give it a try, or something!
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```
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//======= Copyright (c) 2015-2020 Vera Visions LLC. All rights reserved. =======
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//
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// Purpose:
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//
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// Example surface
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//==============================================================================
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!!ver 110
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!!samps diffuse
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#include "sys/defs.h"
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varying vec2 tex_c;
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#ifdef VERTEX_SHADER
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void main ()
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{
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tex_c = v_texcoord; /* get our texture coordinates, which we'll use for the texture2D command */
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gl_Position = ftetransform(); /* place vertex into the place FTE wants us to put them at */
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}
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#endif
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#ifdef FRAGMENT_SHADER
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void main ()
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{
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vec4 d_f = texture2D(s_diffuse, tex_c); /* load the fragment from our diffusemap sample */
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// d_f.rgb = vec3(1.0, 0.0, 0.0); /* turns out fragment (aka pixel) red */
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gl_FragColor = d_f; /* final pixel output is that of d_f */
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}
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#endif
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```
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## Dissecting GLSL shaders
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When we pass `program <shadername>` in our Material, the engine will load `glsl/<shadername>.glsl` to handle the material for us.
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The shader in question needs to define a `main` function for both a vertex and a fragment shader. That's what the **ifdef**s are for in the above example.
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You can not have separate files handle vertex/fragment programs, unlike in **id Tech 4/Doom III**.
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At some point in the `main` function, we do have to set `gl_Position` and `gl_FragColor` respectively. Those can not be undefined.
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