Notes on Adding a New Modifier

source/blender/makesdna/DNA_modifier_types.h

Add a new modifier name to the ModifierType list, e.g. eModifierType_FooBar. Make sure the new entry comes before NUM_MODIFIER_TYPES, but does not modify the ordinal for any other modifier.

I'm not sure that this is 100% required for every possible modifier, but usually you will want to add a new modifier struct to the end of the file:

typedef struct FooBarModifierData {
    ModifierData modifier;
    /* modifier-specific data goes here; remember to add pad if necessary! */
}FooBarModifierData;

This is also a good place to declare flag enumerations and the like.

source/blender/makesrna/RNA_access.h

Add a new StructRNA declaration, e.g. extern StructRNA RNA_FooBarModifier;.

source/blender/makesrna/intern/rna_modifier.c

Add the new modifier to the modifier_type_items array. There are currently four categories it can go under: Modify, Generate, Deform, and Simulate. Entries within a category should be in alphabetical order.

{eModifierType_FooBar, "FOO_BAR", ICON_MODIFIER, "Foo Bar", ""},

Add a RNA define funcion for the new modifier, rna_def_modifier functions are in alphabetical order.

static void rna_def_modifier_foobar(BlenderRNA *brna)
{
	StructRNA *srna;
	PropertyRNA *prop;

	srna = RNA_def_struct(brna, "FooBarModifier", "Modifier");
	RNA_def_struct_ui_text(srna, "FooBar Modifier", "It's a foo modifier");
	RNA_def_struct_sdna(srna, "FooBarModifierData");
	RNA_def_struct_ui_icon(srna, ICON_MODIFIER);
}

In function rna_Modifier_refine, add a new case for the modifier struct:

    case eModifierType_FooBar:
        return &RNA_FooBarModifier;

source/blender/modifiers/MOD_modifiertypes.h

Add a new ModifierTypeInfo declaration, e.g. extern ModifierTypeInfo modifierType_FooBar;

source/blender/modifiers/intern/MOD_util.c

Add a new INIT_TYPE line, e.g. INIT_TYPE(FooBar);.

source/blender/modifiers/intern/MOD_foobar.c

Add a new source file to contain your modifier's code, e.g. MOD_foobar.c.

This source file must contain at least the ModifierTypeInfo definition for your modifier:

ModifierTypeInfo modifierType_FooBar = {
	/* name */              "Foo Bar",
	/* structName */        "FooBarModifierData",
	/* structSize */        sizeof(FooBarModifierData),
	/* type */              eModifierTypeType_Constructive,
	/* flags */             eModifierTypeFlag_AcceptsMesh,

	/* copyData */          NULL,
	/* deformVerts */       NULL,
	/* deformMatrices */    NULL,
	/* deformVertsEM */     NULL,
	/* deformMatricesEM */  NULL,
	/* applyModifier */     applyModifier,
	/* applyModifierEM */   NULL,
	/* initData */          NULL,
	/* requiredDataMask */  NULL,
	/* freeData */          NULL,
	/* isDisabled */        NULL,
	/* updateDepgraph */    NULL,
	/* dependsOnTime */     NULL,
	/* dependsOnNormals */  NULL,
	/* foreachObjectLink */ NULL,
	/* foreachIDLink */     NULL,
	/* foreachTexLink */    NULL,
};

Most of the function pointers can be set to NULL if you don't need it. You probably do want to set the applyModifier function pointer though, in order to output a new DerivedMesh.

source/blender/modifiers/CMakeLists.txt

Add the new file to the SRC variable, e.g. intern/MOD_foobar.c

release/scripts/startup/bl_ui/properties_data_modifier.py

Add a new method to the DATA_PT_modifiers class:

    def FOOBAR(self, layout, ob, md):
        pass

Dev:Source/Modifiers/Adding

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