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Materials

Materials are used to express how a graphical component (a sprite, tilemap, font, GUI node, model etc) should be rendered.

A material holds tags, information that is used in the rendering pipeline to select objects to be rendered. It also holds references to shader programs that are compiled through the available graphics driver and uploaded to the graphics hardware and run when the component is rendered each frame.

Creating a material

To create a material, right click a target folder in the Assets browser and select New… ▸ Material. (You can also select File ▸ New… from the menu, and then select Material). Name the new material file and press Ok.

Material file

The new material will open in the Material Editor.

Material editor

The material file contains the following information:

Name
The identity of the material. This name is used to list the material in the Render resource to include it in the build. The name is also used in the render API function render.enable_material(). The name should be unique.
Vertex Program
The vertex shader program file (.vp) to use when rendering with the material. The vertex shader program is run on the GPU for each of a component’s primitive vertices. It computes the screen position of each vertex and also optionally output “varying” variables that are interpolated and input to the fragment program.
Fragment Program
The fragment shader program file (.fp) to use when rendering with the material. The program runs on the GPU for each of a primitive’s fragments (pixels) and its purpose is to decide the color of each fragment. This is usually done by texture lookups and calculations based on input variables (varying variables or constants).
Vertex Constants
Uniforms that will be passed to the vertex shader program. See below for a list of available constants.
Fragment Constants
Uniforms that will be passed to the fragment shader program. See below for a list of available constants.
Samplers
You can optionally configure specific samplers in the materials file. Add a sampler, name it according to the name used in the shader program and set the wrap and filter settings to your liking.
Tags
The tags associated with the material. Tags are represented in the engine as a bitmask that is used by render.predicate() to collect components that should be drawn together. See the Render documentation on how to do that. The maximum number of tags you can use in a project is 32.

Vertex and fragment constants

Shader constants, or “uniforms” are values that are passed from the engine to vertex and fragment shader programs. To use a constant you define it in the material file as either a Vertex Constant property or a Fragment Constant property. Corresponding uniform variables need to be defined in the shader program. The following constants can be set in a material:

CONSTANT_TYPE_WORLD
The world matrix. Use to transform vertices into world space. For some component types, the vertices are already in world space when they arrive to the vertex program (due to batching). In those cases multiplying with the world matrix in the shader will yield the wrong results.
CONSTANT_TYPE_VIEW
The view matrix. Use to transform vertices to view (camera) space.
CONSTANT_TYPE_PROJECTION
The projection matrix. Use to transform vertices to screen space.
CONSTANT_TYPE_VIEWPROJ
A matrix with the view and projection matrices already multiplied.
CONSTANT_TYPE_WORLDVIEW
A matrix with the world and view projection matrices already multiplied.
CONSTANT_TYPE_NORMAL
A matrix to compute normal orientation. The world transform might include non-uniform scaling, which breaks the orthogonality of the combined world-view transform. The normal matrix is used to avoid issues with the direction when transforming normals. (The normal matrix is the transpose inverse of the world-view matrix).
CONSTANT_TYPE_USER
A vector4 constant that you can use for any custom data you want to pass into your shader programs. You can set the initial value of the constant in the constant definition, but it is mutable through the functions .set_constant() and .reset_constant() for each component type (sprite, model, spine, particlefx and tilemap)

Samplers

Samplers are used to sample the color information from a texture (a tile source or atlas). The color information can then be used for calculations in the shader program.

Sprite, tilemap, GUI and particle effect components automatically gets a sampler2D set. The first declared sampler2D in the shader program is automatically bound to the image referenced in the graphics component. Therefore there is currently no need to specify any samplers in the materials file for those components. Furthermore, those component types currently only support a single texture. (If you need multiple textures in a shader, you can use render.enable_texture() and set texture samplers manually from your render script.)

Sprite sampler

-- mysprite.fp
varying mediump vec2 var_texcoord0;
uniform lowp sampler2D MY_SAMPLER;
void main()
{
    gl_FragColor = texture2D(MY_SAMPLER, var_texcoord0.xy);
}

You can specify a component’s sampler settings by adding the sampler by name in the materials file. If you don’t set up your sampler in the materials file, the global graphics project settings are used.

Sampler settings

For model components, you need to specify your samplers in the material file with the settings you want. The editor will then allow you to set textures for any model component that use the material:

Model samplers

-- mymodel.fp
varying mediump vec2 var_texcoord0;
uniform lowp sampler2D TEXTURE_1;
uniform lowp sampler2D TEXTURE_2;
void main()
{
    lowp vec4 color1 = texture2D(TEXTURE_1, var_texcoord0.xy);
    lowp vec4 color2 = texture2D(TEXTURE_2, var_texcoord0.xy);
    gl_FragColor = color1 * color2;
}

Model

Sampler settings

Name

The name of the sampler. This name should match the sampler2D declared in the fragment shader.

Wrap U/W

The wrap mode for the U and V axes:

  • WRAP_MODE_REPEAT will repeat texture data outside the range [0,1].
  • WRAP_MODE_MIRRORED_REPEAT will repeat texture data outside the range [0,1] but every second repetition is mirrored.
  • WRAP_MODE_CLAMP_TO_EDGE will set texture data for values greater than 1.0 to 1.0, and any values less than 0.0 is set to 0.0—i.e. the edge pixels will be repeated to the edge.
Filter Min/Mag

The filtering for magnification and minification. Nearest filtering requires less computation than linear interpolation, but can result in aliasing artifacts. Linear interpolation often provides smoother results:

  • FILTER_MODE_NEAREST uses the texel with coordinates nearest the center of the pixel.
  • FILTER_MODE_LINEAR sets a weighted linear average of the 2x2 array of texels that lie nearest to the center of the pixel.
  • FILTER_MODE_NEAREST_MIPMAP_NEAREST chooses the nearest texel value within an individual mipmap.
  • FILTER_MODE_NEAREST_MIPMAP_LINEAR selects the nearest texel in the two nearest best choices of mipmaps and then interpolates linearly between these two values.
  • FILTER_MODE_LINEAR_MIPMAP_NEAREST interpolates linearly within an individual mipmap.
  • FILTER_MODE_LINEAR_MIPMAP_LINEAR uses linear interpolation to compute the value in each of two maps and then interpolates linearly between these two values.

Constants buffers

When the rendering pipeline draws, it pulls constant values from a default system constants buffer. You can create a custom constants buffer to override the default constants and instead set shader program uniforms programmatically in the render script:

self.constants = render.constant_buffer() 
self.constants.tint = vmath.vector4(1, 0, 0, 1) 
...
render.draw(self.my_pred, self.constants) 
  1. Create a new constants buffer
  2. Set the tint constant to bright red
  3. Draw the predicate using our custom constants

Note that the buffer’s constant elements are referenced like an ordinary Lua table, but you can’t iterate over the buffer with pairs() or ipairs().


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