![]() ![]() This callback function is invoked immediately from the p5.Geometry constructor as an instance member of the new p5.Geometry instance (i.e. The callback is where the heavy lifting is done. Therefore, if you want your custom geometry to have configurable level of detail which can be described by these parameters then you should add support for them in your geometry callback, and if you don't need level of detail capability then you can ignore these. However, when creating custom geometry there is nothing "magic" about these parameters! They are assigned to properties the p5.Geometry instance, they can be referenced in the callback as tailX and tailY, and they are used by the computeFaces instance method to automatically generate triangles based on the array of vertices (more on this later). For most the built-in primitives the geometry is generated as vertical strips of triangles, so detailX controls the number of strips and detailY controls the number of rows per strip. The detailX and detailY parameters are intended to control the level of detail for the geometry that is generated. The number of vertices to generate in the vertical direction.Ī callback function that will be invoked once and is expected to populate the vertex array. The number of vertices to generate in the horizontal direction. ![]() The p5.Geometry constructor takes three parameters and initializes the geometry, however most of the actual work is done in within the callback function passed as the third parameter. The goal of this article is to fill this gap. Each of its instance methods has only a cursory description, and the expected behavior of the callback function is completely lacking any specification. The p5.Geometry class in p5.js is not particularly well documented. However, it is also possible to generate geometry procedurally within p5.js. One option to create efficient 3D geometry in p5.js is to create it in an external 3D modelling program such as Blender, export the geometry as an OBJ file, and then load it into p5.js using loadModel(). Additionally, complex geometry constructed with beginShape(), vertex(), and endShape(), will definitely not be efficient since the vertex buffers generated for these will not be cached and reused at all. This is because WebGL and GPU are much better optimized when drawing large numbers of triangles as a single call, instead of drawing many smaller sets of triangles separately. However, when you have a large number (thousands) of primitives on screen at once this will not be very fast. The individual 3D primitive functions in p5.js (such as box() and sphere()) do generate and reuse the efficient geometry representation described above. Because of this fact, it is very important for performance that the visible geometry be drawn very efficiently. 3D Geometry in p5.jsīecause p5.js draws graphics in immediate mode, all the triangles that make up the visible geometry must be drawn every frame. This involves having an additional buffer with a list of vertex indices, three per triangle, that specify the index into the vertex buffer for corners of each triangle.įor more information on general concepts about 3D geometry I recommend the Guides available on especially the one about Indexed Vertices. However, there is a more efficient way to represent geometry because often times multiple triangles will share the same vertex. The simplest way to draw geometry is to store it such that for every triangle all of its corners are listed independently in the various buffers. Triangle corner positions, texture coordinates, and normals are stored as arrays of numbers (3D vectors are unpacked into the array so that instead of a multi-dimensional array, or an array of arrays, you just have an array with 3 values per vector). However, in order to harness this performance, the triangles that make up that scene must be prepared some very particular data structures. Graphics cards, and the APIs that allow programs to utilize them, are very efficient at drawing huge numbers of triangles every frame while still maintaining a high framerate. The normal is a 3D vector, meaning it represents a direction rather than a position, that indicates the degree to which that part of the triangle should be illuminated when a light is shining on it from a certain direction. The texture coordinate is a 2D coordinate that specifies what part of the texture image should be mapped to that point. In addition to a position in 3D space, each vertex has a texture coordinate, and a normal. In the context of this article 3D geometry is a set of triangles each defined by three corners, called vertices, in three-dimensional space. A guide to creating custom, procedurally generated three-dimensional geometry in a way that renders performantly using the p5.Geometry class. ![]()
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