Py API Docs: More gpu module documentation
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@ -11,7 +11,10 @@ This makes them much faster than using the legacy `glBegin` and `glEnd` method,
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Every batch has a so called `Vertex Buffer`.
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It contains the attributes for every vertex.
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Typical attributes are `position`, `color` and `uv`.
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Which attributes the vertex buffer of a batch contains, depends on the shader that will be used to process the batch.
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Which attributes the vertex buffer of a batch contains, depends on the shader that will be used to process the batch. The best way to create a new batch is to use the :class:`gpu_extras.batch.batch_for_shader` function.
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Furthermore, when creating a new batch, you have to specify the draw type.
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The most used types are ``POINTS``, ``LINES`` and ``TRIS``.
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Shaders
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+++++++
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@ -38,6 +41,68 @@ The attributes and uniforms used by built-in shaders are listed here: :class:`gp
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A batch can only be processed/drawn by a shader when it provides all the attributes that the shader specifies.
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Vertex Buffers
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++++++++++++++
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A vertex buffer is an array that contains the attributes for every vertex.
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To create a new vertex buffer (:class:`gpu.types.GPUVertBuf`) you have to provide two things: 1) the amount of vertices in the buffer and 2) the format of the buffer.
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The format (:class:`gpu.types.GPUVertFormat`) describes which attributes are stored in the buffer.
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E.g. to create a vertex buffer that contains 6 vertices, each with a position and a normal could look like so::
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import gpu
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vertex_positions = [(0, 0, 0), ...]
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vertex_normals = [(0, 0, 1), ...]
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fmt = gpu.types.GPUVertFormat()
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fmt.attr_add(id="pos", comp_type='F32', len=3, fetch_mode='FLOAT')
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fmt.attr_add(id="normal", comp_type='F32', len=3, fetch_mode='FLOAT')
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vbo = gpu.types.GPUVertBuf(len=6, format=fmt)
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vbo.attr_fill(id="pos", data=vertex_positions)
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vbo.attr_fill(id="normal", data=vertex_normals)
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batch = gpu.types.GPUBatch(type='TRIS', buf=vbo)
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This batch contains two triangles now.
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Vertices 0-2 describe the first and vertices 3-5 the second triangle.
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.. note::
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The recommended way to create batches is to use the :class:`gpu_extras.batch.batch_for_shader` function. It makes sure that you provide all the vertex attributes that are necessary to be able to use a specific shader.
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Index Buffers
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+++++++++++++
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The main reason why index buffers exist is to reduce the amount of memory required to store and send geometry.
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E.g. often the same vertex is used by multiple triangles in a mesh.
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Instead of vertex attributes multiple times to the gpu, an index buffer can be used.
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An index buffer is an array of integers that describes in which order the vertex buffer should be read.
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E.g. when you have a vertex buffer ``[a, b, c]`` and an index buffer ``[0, 2, 1, 2, 1, 0]`` it is like if you just had the vertex buffer ``[a, c, b, c, b, a]``.
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Using an index buffer saves memory because usually a single integer is smaller than all attributes for one vertex combined.
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Index buffers can be used like so::
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indices = [(0, 1), (2, 0), (2, 3), ...]
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ibo = gpu.types.GPUIndexBuf(type='LINES', seq=indices)
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batch = gpu.types.GPUBatch(type='LINES', buf=vbo, elem=ibo)
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.. note::
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Instead of creating index buffers object manually, you can also just use the optional `indices` parameter of the :class:`gpu_extras.batch.batch_for_shader` function.
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Offscreen Rendering
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+++++++++++++++++++
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Everytime something is drawn, the result is written into a framebuffer.
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Usually this buffer will later be displayed on the screen.
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However, sometimes you might want to draw into a separate "texture" and use it further.
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E.g. you could use the render result as a texture on another object or save the rendered result on disk.
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Offscreen Rendering is done using the :class:`gpu.types.GPUOffScreen` type.
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.. warning::
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``GPUOffScreen`` objects are bound to the opengl context they have been created in.
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This also means that once Blender discards this context (i.e. a window is closed) the offscreen instance will also be freed.
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Examples
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++++++++
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