Orx Learning

Shader module. Allows the definition of shader information (code + parameters).

[ShaderTemplate]
Code = "// Shader code
  void main()
  {
   // Do stuff
  }"
CodeList       = CodeKey1 # ... # CodeKeyN 
ParamList      = Param1 # ... # ParamN
ParamFloat     = <float>
ParamVector    = <vector>
ParamTexture   = path/to/texture
UseCustomParam = <bool>
KeepInCache    = <bool>

Here's a list of the available properties for an orxSHADER structure:

• Code: Used to declare a monolithic shader. Will be ignored if CodeList is defined. This block ¹⁾ contains the code that will be executed. It needs to be provided and be valid GLSL fragment shader code.
• CodeList: The values of this list will be used as config keys from this section to reconstruct, in the given order, a multi-part shader. If not defined, Code will be used instead.
• KeepInCache: Defines if the shader code should be kept in memory even if no shader of this type is currently in use. This saves time (reading from disk + compiling) but costs memory. Its default value is false.
• ParamList: Define all the parameters your shader code needs. Defined params then must have a default value to guess their type: textures, vectors and floats are supported. If none is provided, type defaults to texture and will use shader's owner texture as value. If an invalid path is provided for a parameter, or the parameter isn't defined at all, the owner's texture will be used ²⁾. If an explicit list is provided for any parameter, the shader variable will be an array of this parameter type (instead of a regular variable) and its size will be the number of items in the list.
• UseCustomParam: When set to true, an event will be sent to override params values at runtime as well as the automated “time” value. Defaults to false, ie. no runtime override unless “time” is used for a float param.

Here's a simple example of a non-interactive shader as seen in the spawner/shader tutorial.

[Decompose]
Code = "void main()
{
  float fRed, fGreen, fBlue;
 
  // Computes positions with offsets
  vec2 vRedPos    = vec2(gl_TexCoord[0].x + offset.x, gl_TexCoord[0].y + offset.y);
  vec2 vGreenPos  = vec2(gl_TexCoord[0].x, gl_TexCoord[0].y);
  vec2 vBluePos   = vec2(gl_TexCoord[0].x - offset.x, gl_TexCoord[0].y - offset.y);
 
  // Red pixel inside texture?
  if((vRedPos.x >= 0.0) && (vRedPos.x <= 1.0) && (vRedPos.y >= 0.0) && (vRedPos.y <= 1.0))
  {
    // Gets its value
    fRed = texture2D(texture, vRedPos).r;
  }
 
  // Green  pixel inside texture?
  if((vGreenPos.x >= 0.0) && (vGreenPos.x <= 1.0) && (vGreenPos.y >= 0.0) && (vGreenPos.y <= 1.0))
  {
    // Gets its value
    fGreen = texture2D(texture, vGreenPos).g;
  }
 
  // Blue pixel inside texture?
  if((vBluePos.x >= 0.0) && (vBluePos.x <= 1.0) && (vBluePos.y >= 0.0) && (vBluePos.y <= 1.0))
  {
    // Gets its value
    fBlue = texture2D(texture, vBluePos).b;
  }
 
  // Outputs the final decomposed pixel
  gl_FragColor = vec4(fRed, fGreen, fBlue, 1.0);
}"
ParamList = texture # offset
offset    = (-0.05, -0.05, 0.0) ~ (0.05, 0.05, 0.0); <= Let's take some random offset

Please see the Shader Tutorials and Shader Examples for more information.

Shader parameters can be defined on the fly if

UseCustomParam = true

is set in your shader. An event of type orxEVENT_TYPE_SHADER and ID orxSHADER_EVENT_SET_PARAM will be fired for all parameters and its payload will contain the name of the param and its default value. Event handler can then modify that value if need be, and it'll get used by the shader.

However, when UseCustomParam is defined to true, those objects can't be batched at rendering, making the rendering phase more expensive. The severity of the processing penalty depends on how many affected objects are displayed. See the test/playground code, orxBounce, for an example on how to set those shader parameters on the fly.

“time” is a keyword recognized by orx: the parameter value will be the object's “age”, in seconds. Example:

ParamList = fTime
fTime = time 

There is an internal texture called pixel. It can be used to specify an image of arbitrary size when used with the Scale property of the object:

[Object]
Graphic = MyTexture
Scale = (16, 16, 1)
 
[MyTexture]
Texture = pixel

In the example above, an Object has a Graphic that will span over 16×16 pixels.

Shaders contain implicit parameters containing owner's texture coordinates. For example:

[GameObject]
Graphic = @
Texture = ObjectTexture.png 
TextureOrigin = (16, 16, 0)
TextureSize = (8, 8, 0)
ShaderList = Shader
 
[Shader]
ParamList = MyTexture # ...
Code = ...

Then orx will generate extra parameters behind the scene regarding the texture MyTexture. The names follow the pattern:

<NameOfTexture>_top, <NameOfTexture>_left,
<NameOfTexture>_bottom, <NameOfTexture>_right

In the above example, the names will then be:

MyTexture_top, MyTexture_left, MyTexture_bottom, MyTexture_right

If MyTexture's dimensions are 32×32, we'd then get:

MyTexture_top = 16 / 32 => 0.5
MyTexture_left = 16 / 32 => 0.5
MyTexture_bottom = (16 + 8) / 32 => 0.75
MyTexture_right = (16 + 8) / 32 => 0.75