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-rw-r--r--sdl2/surface.scm41
1 files changed, 22 insertions, 19 deletions
diff --git a/sdl2/surface.scm b/sdl2/surface.scm
index 24846c2..4eb5212 100644
--- a/sdl2/surface.scm
+++ b/sdl2/surface.scm
@@ -79,37 +79,40 @@ PROC."
(bytevector-sint-ref (pointer->bytevector pointer %int-size offset)
0 (native-endianness) %int-size))
-;; The offsets below correspond to the SDL_Surface struct elements
-;; that come before the element in question.
-(define %width-offset (sizeof (list uint32 '*)))
-(define %height-offset (sizeof (list uint32 '* int)))
-(define %pitch-offset (sizeof (list uint32 '* int int)))
-(define %pixels-offset 32)
+;; A partial list of surface types so that we can parse the data we
+;; need out of the SDL_Surface struct pointer.
+(define %surface-types
+ (list uint32 ; flags
+ '* ; format
+ int ; width
+ int ; height
+ int ; pitch
+ '*)) ; pixels
+
+(define-syntax-rule (surface-parse-match surface matchers ...)
+ (match (parse-c-struct (unwrap-surface surface) %surface-types)
+ matchers ...))
(define (surface-width surface)
"Return the width of SURFACE in pixels."
- (pointer-int-ref (unwrap-surface surface) %width-offset))
+ (surface-parse-match surface
+ ((_ _ width _ _ _) width)))
(define (surface-height surface)
"Return the height of SURFACE in pixels."
- (pointer-int-ref (unwrap-surface surface) %height-offset))
+ (surface-parse-match surface
+ ((_ _ _ height _ _) height)))
(define (surface-pitch surface)
"Return the length of a row of pixels in SURFACE in bytes."
- (pointer-int-ref (unwrap-surface surface) %pitch-offset))
+ (surface-parse-match surface
+ ((_ _ _ _ pitch _) pitch)))
(define (surface-pixels surface)
"Return a bytevector containing the raw pixel data in SURFACE."
- (let* ((ptr (unwrap-surface surface))
- (height (pointer-int-ref ptr %height-offset))
- (pitch (pointer-int-ref ptr %pitch-offset))
- (pixels-ptr (pointer->bytevector ptr %pointer-size %pixels-offset))
- (pixels (make-pointer
- (bytevector-uint-ref pixels-ptr
- 0
- (native-endianness)
- %pointer-size))))
- (pointer->bytevector pixels (* height pitch))))
+ (surface-parse-match surface
+ ((_ _ _ height pitch pixels)
+ (pointer->bytevector pixels (* height pitch)))))
(define (symbol->sdl-pixel-format sym)
(match sym