PyAPI: gpu utility module to create new batches

Support the common case of creating batches from python geometry,
a shader and optionally indices.

See D3779

release/scripts/modules/gpu_extras/__init__.py

@@ -17,5 +17,6 @@
 # ***** END GPL LICENSE BLOCK *****
 
 __all__ = (
+    "batch",
     "presets",
 )

release/scripts/modules/gpu_extras/batch.py

@@ -0,0 +1,62 @@
+# ***** BEGIN GPL LICENSE BLOCK *****
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software Foundation,
+# Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+# ***** END GPL LICENSE BLOCK *****
+
+__all__ = (
+    "batch_for_shader"
+)
+
+
+def batch_for_shader(shader, type, content, indices=None):
+    """
+    Return a batch already configured and compatible with the shader.
+
+    :arg shader: shader for which a compatible format will be computed.
+    :type shader: :class:`gpu.types.GPUShader`
+    :arg type: "'POINTS', 'LINES', 'TRIS' or 'LINES_ADJ'".
+    :type type: str
+    :arg content: Maps the name of the shader attribute with the data to fill the vertex buffer.
+    :type content: dict
+    :return: compatible batch
+    :rtype: :class:`gpu.types.Batch`
+    """
+    import gpu
+    from gpu.types import (
+        GPUBatch,
+        GPUIndexBuf,
+        GPUVertBuf,
+    )
+
+    for data in content.values():
+        vbo_len = len(data)
+        break
+    else:
+        raise ValueError("Empty 'content'")
+
+    vbo_format = shader.format_calc()
+    vbo = GPUVertBuf(vbo_format, vbo_len)
+
+    for id, data in content.items():
+        if len(data) != vbo_len:
+            raise ValueError("Length mismatch for 'content' values")
+        vbo.attr_fill(id, data)
+
+    if indices is None:
+        return GPUBatch(type=type, buf=vbo)
+    else:
+        ibo = GPUIndexBuf(type=type, seq=indices)
+        return GPUBatch(type=type, buf=vbo, elem=ibo)