mirror of https://github.com/kivy/kivy.git
102 lines
3.2 KiB
ReStructuredText
102 lines
3.2 KiB
ReStructuredText
.. _graphics:
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Graphics
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========
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Introduction to Canvas
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----------------------
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Widgets graphical representation is done using a canvas, which you can see both
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as an unlimited drawing board, and as a set of drawing instructions, there are
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numerous different instructions you can apply (add) to your canvas, but there
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is two main kind of them:
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- :mod:`kivy.graphics.context_instructions` Context instructions
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- :mod:`kivy.graphics.vertex_instructions` Vertex Instructions
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Context instructions don't draw anything, but they change the results of the
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Vertex instructions.
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Canvas can contains subsets of instructions, to treat them specially. There are
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two default subsets of this kind, that you can access as `canvas.before` and
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`canvas.after`, the instructions in these groups will be executed respectively
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before and after the main ones, which mean they will be respectively under and
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above them.
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to add a canvas instruction to a widget, you use the canvas context::
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class MyWidget(Widget):
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def __init__(self, **kwargs):
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super(MyWidget, self).__init__(**kwargs)
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with self.canvas:
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# add your instruction for main canvas here
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with self.canvas.before:
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# you can use this to add instructions rendered before
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with self.canvas.after:
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# you can use this to add instructions rendered after
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Context instructions
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--------------------
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Context instructions manipulate the opengl context, you can rotate, translate,
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and scale your canvas, attach a texture or change the drawing color, this one
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is the most commonly used, but others are really useful too::
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with self.canvas.before:
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Color(1, 0, .4, mode='rgb')
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Drawing instructions
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--------------------
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Drawing instructions are ranging from very simple ones, to draw a line or a
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polygon, to more complex ones, like meshes or bezier curves::
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with self.canvas:
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# draw a line using the default color
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Line(points=(x1, y1, x2, y2, x3, y3))
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# lets draw a semi-transparent red square
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Color(1, 0, 0, .5, mode='rgba')
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Rect(pos=self.pos, size=self.size)
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Manipulating instructions
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-------------------------
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Sometime, you want to update or remove the instructions you added to a canvas,
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this can be done in various ways depending on your needs:
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You can keep a reference to your instruction and update them::
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class MyWidget(Widget):
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def __init__(self, **kwargs):
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super(MyWidget, self).__init__(**kwargs)
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with self.canvas:
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self.rect = Rectangle(pos=self.pos, size=self.size)
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self.bind(pos=self.update_rect)
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self.bind(size=self.update_rect)
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def update_rect(self, *args):
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self.rect.pos = self.pos
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self.rect.size = self.size
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Or you can clean your canvas and start fresh::
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class MyWidget(Widget):
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def __init__(self, **kwargs):
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super(MyWidget, self).__init__(**kwargs)
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self.draw_my_stuff()
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self.bind(pos=self.draw_my_stuff)
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self.bind(size=self.draw_my_stuff)
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def draw_my_stuff(self):
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self.canvas.clear()
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with self.canvas:
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self.rect = Rectangle(pos=self.pos, size=self.size)
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