# -*- coding: utf-8 -*- # Copyright (c) 2015, Vispy Development Team. # Distributed under the (new) BSD License. See LICENSE.txt for more info. from __future__ import division from .linear import NullTransform, STTransform from ._util import TransformCache class TransformSystem(object): """ TransformSystem encapsulates information about the coordinate systems needed to draw a Visual. Visual rendering operates in four coordinate systems: * **Visual** - arbitrary local coordinate frame of the visual. Vertex buffers used by the visual are usually specified in this coordinate system. * **Document** - This coordinate system has units of _logical_ pixels, and should usually represent the pixel coordinates of the canvas being drawn to. Visuals use this coordinate system to make measurements for font size, line width, and in general anything that is specified in physical units (px, pt, mm, in, etc.). Note that, by convention, _logical_ pixels are not necessarily the same size as the _physical_ pixels in the framebuffer that is being rendered to. * **Buffer** - The buffer coordinate system has units of _physical_ pixels, and should usually represent the coordinates of the current framebuffer being rendered to. Visuals use this coordinate system primarily for antialiasing calculations. In most cases, this will have the same scale as the document coordinate system because the active framebuffer is the back buffer of the canvas, and the canvas will have _logical_ and _physical_ pixels of the same size. The scale may be different in the case of high-resolution displays, or when rendering to an off-screen framebuffer with different scaling or boundaries than the canvas. * **Render** - This coordinate system is the obligatory system for vertexes returned by a vertex shader. It has coordinates (-1, -1) to (1, 1) across the current glViewport. In OpenGL terminology, this is called normalized device coordinates. Parameters ---------- canvas : Canvas The canvas being drawn to. dpi : float The dot-per-inch resolution of the document coordinate system. By default this is set to the resolution of the canvas. Notes ----- By default, TransformSystems are configured such that the document coordinate system matches the logical pixels of the canvas, Examples -------- Use by Visuals ~~~~~~~~~~~~~~ 1. To convert local vertex coordinates to normalized device coordinates in the vertex shader, we first need a vertex shader that supports configurable transformations:: vec4 a_position; void main() { gl_Position = $transform(a_position); } Next, we supply the complete chain of transforms when drawing the visual: def draw(tr_sys): tr = tr_sys.get_full_transform() self.program['transform'] = tr.shader_map() self.program['a_position'] = self.vertex_buffer self.program.draw('triangles') 2. Draw a line whose width is given in mm. To start, we need normal vectors for each vertex, which tell us the direction the vertex should move in order to set the line width:: vec4 a_position; vec4 a_normal; float u_line_width; float u_dpi; void main() { // map vertex position and normal vector to the document cs vec4 doc_pos = $visual_to_doc(a_position); vec4 doc_normal = $visual_to_doc(a_position + a_normal) - doc_pos; // Use DPI to convert mm line width to logical pixels float px_width = (u_line_width / 25.4) * dpi; // expand by line width doc_pos += normalize(doc_normal) * px_width; // finally, map the remainder of the way to normalized device // coordinates. gl_Position = $doc_to_render(a_position); } In this case, we need to access the transforms independently, so ``get_full_transform()`` is not useful here:: def draw(tr_sys): # Send two parts of the full transform separately self.program['visual_to_doc'] = tr_sys.visual_to_doc.shader_map() doc_to_render = (tr_sys.framebuffer_to_render * tr_sys.document_to_framebuffer) self.program['visual_to_doc'] = doc_to_render.shader_map() self.program['u_line_width'] = self.line_width self.program['u_dpi'] = tr_sys.dpi self.program['a_position'] = self.vertex_buffer self.program['a_normal'] = self.normal_buffer self.program.draw('triangles') 3. Draw a triangle with antialiasing at the edge. 4. Using inverse transforms in the fragment shader Creating TransformSystem instances ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1. Basic example, including checks for canvas resolution 2. How to handle off-screen framebuffers """ def __init__(self, canvas, dpi=None): self._canvas = canvas self._cache = TransformCache() if dpi is None: dpi = canvas.dpi self._dpi = dpi # Null by default; visuals draw directly to the document coordinate # system. self._visual_to_document = NullTransform() self._document_to_framebuffer = STTransform() self._framebuffer_to_render = STTransform() self.auto_configure() def auto_configure(self): """Automatically configure the TransformSystem: * document_to_framebuffer maps from the Canvas logical pixel coordinate system to the framebuffer coordinate system, assuming physical pixels of the same size. The y-axis is inverted in this transform. * framebuffer_to_render maps from the framebuffer coordinate system to normalized device coordinates (-1 to 1). """ # By default, this should invert the y axis -- no difference between # the scale of logical and physical pixels. canvas = self._canvas map_from = [(0, 0), canvas.size] map_to = [(0, canvas.size[1]), (canvas.size[0], 0)] self._document_to_framebuffer.set_mapping(map_from, map_to) # Automatically configure buffer coordinate system to match the canvas map_from = [(0, 0), canvas.size] map_to = [(-1, -1), (1, 1)] self._framebuffer_to_render.set_mapping(map_from, map_to) @property def canvas(self): """ The Canvas being drawn to. """ return self._canvas @property def dpi(self): """ Physical resolution of the document coordinate system (dots per inch). """ return self._dpi @dpi.setter def dpi(self, dpi): assert dpi > 0 self._dpi = dpi @property def visual_to_document(self): """ Transform mapping from visual local coordinate frame to document coordinate frame. """ return self._visual_to_document @visual_to_document.setter def visual_to_document(self, tr): if self._visual_to_document is not tr: self._visual_to_document = tr @property def document_to_framebuffer(self): """ Transform mapping from document coordinate frame to the framebuffer (physical pixel) coordinate frame. """ return self._document_to_framebuffer @document_to_framebuffer.setter def document_to_framebuffer(self, tr): if self._document_to_framebuffer is not tr: self._document_to_framebuffer = tr @property def framebuffer_to_render(self): """ Transform mapping from pixel coordinate frame to rendering coordinate frame. """ return self._framebuffer_to_render @framebuffer_to_render.setter def framebuffer_to_render(self, tr): if self._framebuffer_to_render is not tr: self._framebuffer_to_render = tr def get_full_transform(self): """ Convenience method that returns the composition of all three transforms:: framebuffer_to_render * document_to_framebuffer * visual_to_document This is used for visuals that do not require physical measurements or antialiasing. """ # noqa return self._cache.get([self.framebuffer_to_render, self.document_to_framebuffer, self.visual_to_document])