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Multi-Pass Rendering ​

Overview ​

Multi-pass rendering is a technique used to render a model multiple times with different materials. This technique is used to achieve effects that are not possible with a single pass. For example, when an entity needs to set it's own stencil.

Example ​

This technique is best explained with a stencil example. In this case, we want an entity outline that is visible through walls. If you just apply a depth function to the outline to make it always render, it will render over the base. This means that you need to use the base to set a stencil and then read it from the outline to ensure it only renders where it should.

In this example material: The base material, sets a stencil value. The outline material inverts its culling and removes the fancy define to give it the visual effect of an outline. It also reads the stencil value and is hidden where the stencil is set.

json
// materials/entity.material
"outline_base:entity_alphatest": {
	"+states": [
		"EnableStencilTest",
		"StencilWrite"
	],
	"frontFace": {
		"stencilFunc": "Always",
		"stencilFailOp": "Replace",
		"stencilDepthFailOp": "Replace",
		"stencilPassOp": "Replace"
	},
	"backFace": {
		"stencilFunc": "Always",
		"stencilFailOp": "Replace",
		"stencilDepthFailOp": "Replace",
		"stencilPassOp": "Replace"
	},
	"stencilRef": 2
},
"outline_outline:entity_alphatest": {
	"+states": [
		"EnableStencilTest",
		"InvertCulling"
	],
	"-states": [
		"DisableCulling"
	],
	"-defines": [
		"FANCY"
	],
	"depthFunc": "Always",
	"frontFace": {
		"stencilFunc": "NotEqual"
	},
	"backFace": {
		"stencilFunc": "Equal"
	},
	"stencilRef": 2,
	"stencilReadMask": 2
}

Each "pass" requires it's own render controller and in this example, they both make use of part_visibility which is used for two reasons:

  • As touched on in Multi-Material Models, when using wild cards to match bones for material configeration, it can bleed into unintended bones (this is not required, It could use base* to apply the material but this way, we get a real-world example).
  • The second reason is that the same model is used for both passes, so without hiding the outline, it would be the only thing visible.

In the outline controller, the ignore_lighting field is set to true to ensure the outline is always rendered at full brightness. The overlay_color field is set to white to allow us to use only one texture or to let us apply some sort of colour wheel effect to the outline.

json
// render_controllers/entity_name.json
{
    "format_version": "1.10.0",
    "render_controllers": {
        "controller.render.outline.base": {
            "geometry": "geometry.default",
            "materials": [
                {
                    "*": "material.base"
                }
            ],
            "textures": [
                "texture.default"
            ],
            "part_visibility": [
                {
                    "*": false
                },
                {
                    "base*": true
                }
            ]
        },
        "controller.render.outline.outline": {
            "geometry": "geometry.default",
            "materials": [
                {
                    "*": "material.outline"
                }
            ],
            "textures": [
                "texture.default"
            ],
            "part_visibility": [
                {
                    "*": false
                },
                {
                    "outline*": true
                }
            ],
            "ignore_lighting": true,
            "overlay_color": {
                "r": 1,
                "g": 1,
                "b": 1,
                "a": 1
            }
        }
    }
}

In the client-entity file, the base is rendered first to ensure that the stencil is set, and then the outline is rendered.

json
// entity.json
"render_controllers": [
	"controller.render.outline.base",   // sets the stencil
	"controller.render.outline.outline" // reads the stencil
]