From cd5bd61bfd9e41f9c6112d98ceae9b340b4b60ef Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Wed, 7 Apr 2021 17:06:08 -0400
Subject: graphics: Fix texture data being upside down.

---
 chickadee/graphics/font.scm    |  2 +-
 chickadee/graphics/sprite.scm  | 18 ++++++++----------
 chickadee/graphics/texture.scm |  9 +++++----
 chickadee/graphics/tiled.scm   | 14 ++++++++++++--
 4 files changed, 26 insertions(+), 17 deletions(-)

diff --git a/chickadee/graphics/font.scm b/chickadee/graphics/font.scm
index 8adba8d..3635676 100644
--- a/chickadee/graphics/font.scm
+++ b/chickadee/graphics/font.scm
@@ -126,7 +126,7 @@ display it at POINT-SIZE.  By default, the ASCII character is used."
                     (row height))
           (let ((gray (u8vector-ref glyph-pixels
                                     (+ (* row pitch) column)))
-                (offset (+ (* (+ y row) texture-size 4)
+                (offset (+ (* (- height (+ y row) 1) texture-size 4)
                            (* (+ x column) 4))))
             (u8vector-set! pixels offset 255)
             (u8vector-set! pixels (+ offset 1) 255)
diff --git a/chickadee/graphics/sprite.scm b/chickadee/graphics/sprite.scm
index 8ab12f9..3a30d49 100644
--- a/chickadee/graphics/sprite.scm
+++ b/chickadee/graphics/sprite.scm
@@ -122,13 +122,11 @@ void main (void) {
              (t1 (rect-y texcoords))
              (s2 (+ (rect-x texcoords) (rect-width texcoords)))
              (t2 (+ (rect-y texcoords) (rect-height texcoords))))
-        ;; Texture origin is at the top-left, so we need to flip the Y
-        ;; coordinate relative to the vertices.
         (sprite-vertex-append! geometry
-                               (x1 y1 s1 t2)
-                               (x2 y1 s2 t2)
-                               (x2 y2 s2 t1)
-                               (x1 y2 s1 t1))
+                               (x1 y1 s1 t1)
+                               (x2 y1 s2 t1)
+                               (x2 y2 s2 t2)
+                               (x1 y2 s1 t2))
         (geometry-index-append! geometry 0 3 2 0 2 1)))
     (with-graphics-state ((g:blend-mode blend-mode)
                           (g:texture-0 texture))
@@ -299,10 +297,10 @@ texture may be specified via the TEXTURE-REGION argument."
          (b (color-b tint))
          (a (color-a tint)))
     (batched-sprite-append! geometry
-                            (x1 y1 s1 t2 r g b a)
-                            (x2 y2 s2 t2 r g b a)
-                            (x3 y3 s2 t1 r g b a)
-                            (x4 y4 s1 t1 r g b a))
+                            (x1 y1 s1 t1 r g b a)
+                            (x2 y2 s2 t1 r g b a)
+                            (x3 y3 s2 t2 r g b a)
+                            (x4 y4 s1 t2 r g b a))
     (geometry-index-append! geometry
                             vertex-offset
                             (+ vertex-offset 3)
diff --git a/chickadee/graphics/texture.scm b/chickadee/graphics/texture.scm
index 3ced853..24aa0f5 100644
--- a/chickadee/graphics/texture.scm
+++ b/chickadee/graphics/texture.scm
@@ -248,9 +248,9 @@ the given MIN-FILTER and MAG-FILTER."
   ;; Convert to 32 bit RGBA color.
   (sdl2:call-with-surface (sdl2:convert-surface-format surface 'abgr8888)
     (lambda (surface)
-      (let* ((width (sdl2:surface-width surface))
-             (height (sdl2:surface-height surface))
-             (pixels (sdl2:surface-pixels surface)))
+      (let ((width (sdl2:surface-width surface))
+            (height (sdl2:surface-height surface))
+            (pixels (sdl2:surface-pixels surface)))
         ;; Zero the alpha channel of pixels that match the transparent
         ;; color key.
         (when transparent-color
@@ -263,7 +263,8 @@ the given MIN-FILTER and MAG-FILTER."
                          (= g (bytevector-u8-ref pixels (+ i 1)))
                          (= b (bytevector-u8-ref pixels (+ i 2))))
                 (bytevector-u8-set! pixels (+ i 3) 0)))))
-        (make-texture pixels width height
+        (make-texture (flip-pixels-vertically pixels width height)
+                      width height
                       #:min-filter min-filter
                       #:mag-filter mag-filter
                       #:wrap-s wrap-s
diff --git a/chickadee/graphics/tiled.scm b/chickadee/graphics/tiled.scm
index 6500a17..2692418 100644
--- a/chickadee/graphics/tiled.scm
+++ b/chickadee/graphics/tiled.scm
@@ -240,12 +240,21 @@
           (duration (attr node 'duration string->number)))
       ;; TODO: lookup actual tile in tileset
       (%make-animation-frame tile-id duration)))
+  (define (atlas-ref atlas id rows columns)
+    ;; Tiled enumerates tiles from the top-left of the tileset image,
+    ;; but here in OpenGL land the origin is in the bottom-left, so we
+    ;; have to do some math invert the rows.
+    (texture-atlas-ref atlas
+                       (+ (* (- rows (floor (/ id columns)) 1)
+                             columns)
+                          (modulo id columns))))
   (define (parse-tile node rows columns atlas batch)
     (let ((id (attr node 'id string->number))
           (animation (map parse-frame ((sxpath '(animation frame)) node)))
           (properties (map parse-property
                            ((sxpath '(properties property)) node))))
-      (%make-tile id (texture-atlas-ref atlas id) batch animation properties)))
+      (%make-tile id (atlas-ref atlas id rows columns)
+                  batch animation properties)))
   (define (parse-tiles nodes size columns atlas batch)
     (let ((table (make-hash-table))
           (tiles (make-vector size))
@@ -257,7 +266,8 @@
       (for-range ((i size))
         (let ((tile
                (or (hash-ref table i)
-                   (%make-tile i (texture-atlas-ref atlas i) batch #f '()))))
+                   (%make-tile i (atlas-ref atlas i rows columns)
+                               batch #f '()))))
           (vector-set! tiles i tile)))
       tiles))
   (define (first-gid node)
-- 
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