render: texture: Add texture region data type.

* chickadee/render/texture.scm (<texture-region>): New record type.

1 files changed, 35 insertions, 0 deletions

diff --git a/chickadee/render/texture.scm b/chickadee/render/texture.scm
index e019aa7..c37fef9 100644
--- a/chickadee/render/texture.scm
+++ b/chickadee/render/texture.scm
@@ -48,6 +48,14 @@
             texture-set!
             texture-ref
 
+            make-texture-region
+            texture-region?
+            texture-region-texture
+            texture-region-x
+            texture-region-y
+            texture-region-width
+            texture-region-height
+
             texture-atlas
             list->texture-atlas
             split-texture
@@ -219,6 +227,33 @@ magnification.  Valid values are 'nearest and 'linear.  By default,
 
 
 ;;;
+;;; Texture Regions
+;;;
+
+(define-record-type <texture-region>
+  (%make-texture-region texture x y width height gl-rect gl-size)
+  texture-region?
+  (texture texture-region-texture)
+  (x texture-region-x)
+  (y texture-region-y)
+  (width texture-region-width)
+  (height texture-region-height)
+  (gl-rect texture-region-gl-rect)
+  (gl-size texture-region-gl-size))
+
+(define (make-texture-region texture x y width height)
+  "Create a new texture region covering a section of TEXTURE defined
+by the bounding box X, Y, WIDTH, and HEIGHT.  All coordinates are
+measured in pixels and must be integers."
+  (let* ((tw (texture-width texture))
+         (th (texture-height texture))
+         (gl-rect (make-rect (/ x tw) (/ y th)
+                             (/ (+ x width) tw) (/ (+ y height) th))))
+    (%make-texture-region texture x y width height gl-rect
+                          (f32vector width height))))
+
+
+;;;
 ;;; Texture Atlas
 ;;;