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<span id="Sprites"></span><div class="header">
<p>
Next: <a href="Fonts.html" accesskey="n" rel="next">Fonts</a>, Previous: <a href="Textures.html" accesskey="p" rel="prev">Textures</a>, Up: <a href="Graphics.html" accesskey="u" rel="up">Graphics</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
<span id="Sprites-1"></span><h4 class="subsection">5.3.3 Sprites</h4>
<p>For those who are new to this game, a sprite is a 2D rectangular
bitmap that is rendered to the screen. For 2D games, sprites are the
most essential graphical abstraction. They are used for drawing maps,
players, NPCs, items, particles, text, etc.
</p>
<p>In Chickadee, the <code>(chickadee graphics sprite)</code> module provides the
interface for working with sprites. Bitmaps are stored in textures
(see <a href="Textures.html">Textures</a>) and can be used to draw sprites via the
<code>draw-sprite</code> procedure.
</p>
<dl>
<dt id="index-draw_002dsprite">Procedure: <strong>draw-sprite</strong> <em>texture position [#:blend-mode] [#:origin] [#:rect] [#:rotation] [#:scale] [#:shear] [#:tint white]</em></dt>
<dd>
<p>Draw <var>texture</var> at <var>position</var>.
</p>
<p>Optionally, other transformations may be applied to the sprite.
<var>rotation</var> specifies the angle to rotate the sprite, in radians.
<var>scale</var> specifies the scaling factor as a 2D vector. <var>shear</var>
specifies the shearing factor as a 2D vector. All transformations are
applied relative to <var>origin</var>, a 2D vector, which defaults to the
lower-left corner.
</p>
<p><var>tint</var> specifies the color to multiply against all the sprite’s
pixels. By default white is used, which does no tinting at all.
</p>
<p>Alpha blending is used by default but the blending method can be
changed by specifying <var>blend-mode</var>.
</p>
<p>The area drawn to is as big as the texture, by default. To draw to an
arbitrary section of the screen, specify <var>rect</var>.
</p></dd></dl>
<span id="Sprite-Batches"></span><h4 class="subsubsection">5.3.3.1 Sprite Batches</h4>
<p>It’s not uncommon to need to draw hundreds or thousands of sprites
each frame. However, GPUs (graphics processing units) are tricky
beasts that prefer to be sent few, large chunks of data to render
rather than many, small chunks. Using <code>draw-sprite</code> on its own
will involve at least one GPU call <em>per sprite</em>. This is fine
for rendering a few dozen sprites, but will become a serious
bottleneck when rendering hundreds or thousands of sprites. To deal
with this, a technique known as “sprite batching” is used. Instead
of drawing each sprite immediately, the sprite batch will build up a
large buffer of sprites to draw and send them to the GPU all at once.
There is one caveat, however. Batching only works if the sprites
being drawn share a common texture. A good strategy for reducing the
number of different textures is to stuff many bitmaps into a single
image file and create a “texture atlas” (see <a href="Textures.html">Textures</a>) to access
the sub-images within.
</p>
<dl>
<dt id="index-make_002dsprite_002dbatch">Procedure: <strong>make-sprite-batch</strong> <em>texture [#:capacity 256]</em></dt>
<dd><p>Create a new sprite batch for <var>texture</var> with initial space for
<var>capacity</var> sprites. Sprite batches automatically resize when they
are full to accomodate as many sprites as necessary.
</p></dd></dl>
<dl>
<dt id="index-sprite_002dbatch_003f">Procedure: <strong>sprite-batch?</strong> <em>obj</em></dt>
<dd><p>Return <code>#t</code> if <var>obj</var> is a sprite batch.
</p></dd></dl>
<dl>
<dt id="index-sprite_002dbatch_002dtexture">Procedure: <strong>sprite-batch-texture</strong> <em>batch</em></dt>
<dd><p>Return the texture for <var>batch</var>.
</p></dd></dl>
<dl>
<dt id="index-set_002dsprite_002dbatch_002dtexture_0021">Procedure: <strong>set-sprite-batch-texture!</strong> <em>batch texture</em></dt>
<dd><p>Set texture for <var>batch</var> to <var>texture</var>.
</p></dd></dl>
<dl>
<dt id="index-sprite_002dbatch_002dadd_0021">Procedure: <strong>sprite-batch-add!</strong> <em>batch position [#:origin] [:rotation] [#:scale] [#:shear] [#:texture-region] [#:tint <code>white</code>]</em></dt>
<dd>
<p>Add sprite located at <var>position</var> to <var>batch</var>.
</p>
<p>To render a subsection of the batch’s texture, a texture object whose
parent is the batch texture may be specified as <var>texture-region</var>.
</p>
<p>See <code>draw-sprite</code> for information about the other arguments.
</p></dd></dl>
<dl>
<dt id="index-sprite_002dbatch_002dclear_0021">Procedure: <strong>sprite-batch-clear!</strong> <em>batch</em></dt>
<dd><p>Reset size of <var>batch</var> to 0.
</p></dd></dl>
<dl>
<dt id="index-draw_002dsprite_002dbatch">Procedure: <strong>draw-sprite-batch</strong> <em>batch [#:blend-mode]</em></dt>
<dd><p>Render <var>batch</var> using <var>blend-mode</var>. Alpha blending is used by
default.
</p></dd></dl>
<span id="g_t9_002dPatches"></span><h4 class="subsubsection">5.3.3.2 9-Patches</h4>
<p>A 9-patch is a method of rendering a texture so that it can be
stretched to cover an area of any size without becoming distorted.
This is achieved by dividing up the sprite into nine regions:
</p>
<ul>
<li> the center, which can be stretched or tiled horizontally and vertically
</li><li> the four corners, which are never stretched or tiled
</li><li> the left and right sides, which can be stretched or tiled vertically
</li><li> the top and bottom sides, which can be stretched or tiled horizontally
</li></ul>
<p>The most common application of this technique is for graphical user
interface widgets like buttons and dialog boxes which are often
dynamically resizable. By using a 9-patch, they can be rendered at
any size without scaling artifacts. The <code>(chickadee graphics
9-patch)</code> module provides this functionality.
</p>
<dl>
<dt id="index-draw_002d9_002dpatch">Procedure: <strong>draw-9-patch</strong> <em>texture rect [#:margin 0] [#:top-margin margin] [#:bottom-margin margin] [#:left-margin margin] [#:right-margin margin] [#:mode stretch] [#:origin] [#:scale] [#:rotation] [#:blend-mode] [#:tint white]</em></dt>
<dd>
<p>Draw a 9-patch over the area <var>rect</var> using <var>texture</var> whose
stretchable/tileable patches are defined by the given margin
measurements. The corners are never stretched/tiled, the left and
right edges will be stretched/tiled vertically, the top and bottom
edges may be stretched/tiled horizontally, and the center may be
stretched/tiled in both directions.
</p>
<p><var>mode</var> may be either <code>stretch</code> (the default) or <code>tile</code>.
</p>
<p><var>margin</var> specifies the margin size for all sides of the 9-patch.
To make margins of differing sizes, the <var>top-margin</var>,
<var>bottom-margin</var>, <var>left-margin</var>, and <var>right-margin</var>
arguments may be used.
</p>
<p>Refer to <code>draw-sprite</code> for information about the other arguments
as they are the same.
</p></dd></dl>
<hr>
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