diff --git a/TODO b/TODO
index d6d3e38..501e373 100644
--- a/TODO
+++ b/TODO
@@ -17,6 +17,7 @@ Extensions on existing code:
 * core:      run destructors when a task-switch results in leaving the app
 * fs:        support read-only files backed with GetBlockAddress() on fx-CG
 * kernel:    SH4- or G-III-specific linker scripts?
+* render:    Properly document bopti fx. Also make it faster maybe?
 
 Future directions:
 * Audio playback using TSWilliamson's libsnd method
diff --git a/include/gint/display-fx.h b/include/gint/display-fx.h
index 7c7d7db..3835986 100644
--- a/include/gint/display-fx.h
+++ b/include/gint/display-fx.h
@@ -61,6 +61,12 @@ typedef enum
 
 } color_t;
 
+/* Profiles:
+   0: MONO        (1 layer: color)
+   1: ALPHA       (2 layers: color, alpha)
+   2: GRAY        (2 layers: light, dark)
+   3: GRAY_ALPHA  (3 layers: light, dark, alpha) */
+
 //---
 //	Image rendering (bopti)
 //---
@@ -83,10 +89,16 @@ typedef struct
 	uint height	:12;
 
 	/* Raw layer data */
-	uint8_t data[];
+	uint8_t *data;
 
 } GPACKED(4) bopti_image_t;
 
+/* Number of layers in the image. */
+GINLINE static int image_layer_count(int profile)
+{
+	return profile + (profile <= 1);
+}
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/render-fx/bopti.c b/src/render-fx/bopti.c
index 460e88c..51a7f3d 100644
--- a/src/render-fx/bopti.c
+++ b/src/render-fx/bopti.c
@@ -164,8 +164,7 @@ void bopti_render(bopti_image_t const *img, struct rbox *rbox, uint32_t *v1,
 	masks(rbox->visual_x, rbox->visual_x + rbox->width - 1, vm);
 
 	/* Number of layers per profile */
-	static const int layer_count[] = { 1, 2, 2, 3 };
-	int layers = layer_count[img->profile];
+	int layers = image_layer_count(img->profile);
 
 	/* For each pair of consecutive VRAM elements involved, create a mask
 	   from the intersection of the standard vram mask with the shift-mask
@@ -222,7 +221,7 @@ void bopti_render_scsp(bopti_image_t const *img, struct rbox *rbox,
 		(0xffffffff << (32 - rbox->width)) >> (rbox->visual_x & 31);
 
 	/* Number of layers */
-	int layers = img->profile - (img->profile >> 1) + 1;
+	int layers = image_layer_count(img->profile);
 
 	/* Number of longwords to skip between rows of [img] */
 	int img_stride = ((img->width + 31) >> 5) * layers;