From af2872325ed461252303ec8b7987058b664843f1 Mon Sep 17 00:00:00 2001 From: David Thompson Date: Sat, 10 Mar 2018 20:32:18 -0500 Subject: Update Chickadee manual. --- manuals/chickadee/Sprites.html | 109 +++++++++++++++++++++++++++++++++++++++-- 1 file changed, 106 insertions(+), 3 deletions(-) (limited to 'manuals/chickadee/Sprites.html') diff --git a/manuals/chickadee/Sprites.html b/manuals/chickadee/Sprites.html index 700941b..0c114bd 100644 --- a/manuals/chickadee/Sprites.html +++ b/manuals/chickadee/Sprites.html @@ -31,7 +31,7 @@ http://www.texinfo.org/ (GNU Texinfo). - + + @@ -67,12 +90,92 @@ ul.no-bullet {list-style: none}

-Next: , Previous: , Up: Graphics   [Contents][Index]

+Next: , Previous: , Up: Graphics   [Contents][Index]

-

2.4.2 Sprites

+

2.4.3 Sprites

+ +

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. In Chickadee, bitmaps are +stored in textures (see Textures) and can be used to draw sprites +via the draw-sprite procedure. +

+
+
Scheme Procedure: draw-sprite texture region [#:scale] [#:rotation] [#:blend-mode alpha] [#:texture-region] [#:shader]
+
+ +

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 draw-sprite on its own +will involve at least one GPU call per sprite, which will +quickly lead to poor performance. To deal with this, a technique +known as “sprite batching” can be used. Instead of drawing each +sprite immediately, the sprite batch will build up a large of buffer +of sprites to draw and defer rendering until the last possible moment. +Batching isn’t a panacea, though. Batching only works if the sprites +being drawn share as much in common as possible. Every time you draw +a sprite with a different texture or blend mode, the batch will be +sent off to the GPU. Therefore, batching is most useful if you +minimize such changes. A good strategy for reducing texture changes +is to stuff many bitmaps into a single image file and create a +“texture atlas” (see Textures) to access the sub-images within. +

+

Taking advantage of sprite batching in Chickadee is easy, just wrap +the code that is calling draw-sprite a lot in the +with-batched-sprites form. +

+
+
Scheme Syntax: with-batched-sprites body …
+

Use batched rendering for all draw-sprite calls within +body. +

+ +

With a basic sprite abstraction in place, it’s possible to build other +abstractions on top of it. One such example is the “nine patch”. A +nine patch is a sprite that can be rendered at various sizes without +becoming distorted. This is achieved by diving up the sprite into +nine regions: +

+ +

The one caveat is that the bitmap regions must be designed in such a +way so that they are not distorted when stretched along the affected +axes. For example, that means that the top and bottom sides could +have varying colored pixels vertically, but not horizontally. +

+

The most common application of this technique is for graphical user +interface widgets like buttons and dialog boxes. By using a nine +patch, they can be rendered at any size without unappealing scaling +artifacts. +

+
+
Scheme Procedure: draw-nine-patch texture region [#:margin 0] [#:top-margin margin] [#:bottom-margin margin] [#:left-margin margin] [#:right-margin margin] [#:texture-region] [#:scale] [#:rotation] [#:blend-mode alpha] [#:shader]
+
+

Draw a nine patch sprite. A nine patch sprite renders texture +as a width x height rectangle whose stretchable areas are +defined by the given margin measurements top-margin, +bottom-margin, left-margin, and right-margin. The +margin argument may be used to configure all four margins at +once. +

+

Refer to draw-sprite (see Sprites) for information about +the other arguments. +

+ +
+
+

+Next: , Previous: , Up: Graphics   [Contents][Index]

+
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