From 99caef2c816d9d75c5d454640554becf75845ce4 Mon Sep 17 00:00:00 2001
From: Lephenixnoir <sebastien.michelland@protonmail.com>
Date: Sun, 15 Mar 2020 12:11:57 +0100
Subject: [PATCH] separate mono and gray rendering to VRAM on fx-9860G

---
 README.md    |  2 ++
 libimg.h     | 18 +++++++++++++++++-
 src/render.c | 26 ++++++++++++++++++++++++--
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 0976f00..2f81187 100644
--- a/README.md
+++ b/README.md
@@ -70,6 +70,8 @@ img_render_vram(sprite, x, y);
 
 `img_render_vram()`, as every other libimg function, accounts for transparent pixels. Only opaque pixels will be copied to VRAM. This makes it very easy to blend images together by just rendering in sequence.
 
+As a quick note, if you have an image with gray pixels on fx-9860G, you need to use `img_render_vram_gray()` instead (with the same parameters). When using `img_render_vram()`, gray pixels will be approximated as black and white.
+
 ## Creating and destroying new images
 
 Because our converted sprite is read-only, we can't do much more for now. To start working on transforms and cool animations, we need to create new images that can be written to. There are two ways to do this; the first is to create an empty image of a fixed size, and the second is to duplicate an existing image.
diff --git a/libimg.h b/libimg.h
index ebc912c..59ca852 100644
--- a/libimg.h
+++ b/libimg.h
@@ -175,13 +175,29 @@ void img_render(img_t src, img_t dst);
    VRAM supports both monochrome and gray pixels. This function clips the
    rendered image onto the VRAM.
 
-   On fx-CG 50, this functions is exactly equivalent to:
+   This function only renders to black-and-white VRAM. Dark gray and light gray
+   pixels are replaced by black and while, respectively. To render imges under
+   the gray engine, use img_render_vram_gray().
+
+   On fx-CG 50, this function is exactly equivalent to:
      img_render(src, img_at(img_vram(), x, y)).
 
    @src   Source image
    @x @y  Render destination on VRAM */
 void img_render_vram(img_t src, int x, int y);
 
+#ifdef FX9860G
+/* img_render_vram_gray(): Render a gray image to the VRAM
+
+   On fx-9860G, mono and gray rendering code must be separated. This function
+   is the direct equivalent of img_render_vram(), but it renders to the gray
+   VRAM and is suitable for gray images.
+
+   @src   Source image
+   @x @y  Render destination on gray VRAM */
+void img_render_vram_gray(img_t src, int x, int y);
+#endif
+
 
 //---
 // Geometric transforms
diff --git a/src/render.c b/src/render.c
index 41802e7..f5e76ae 100644
--- a/src/render.c
+++ b/src/render.c
@@ -3,6 +3,10 @@
 
 #include <gint/display.h>
 
+#ifdef FX9860G
+#include <gint/gray.h>
+#endif
+
 void img_fill(img_t img, img_pixel_t color)
 {
 	img_pixel_t *px = img.pixels;
@@ -54,8 +58,26 @@ void img_render_vram(img_t img, int x, int y)
 	for(int dy = 0; dy < img.height; dy++, px += img.stride)
 	for(int dx = 0; dx < img.width; dx++)
 	{
-		/* TODO: Render using gray? */
-		dpixel(x+dx, y+dy, px[dx]);
+		img_pixel_t c = px[dx];
+
+		/* Provide a mildly useful approximation of gray rendering.
+		   Seeing the black-and-white approximation might make it more
+		   explicit to the user that mono rendering has been used,
+		   rather than rendering nothing */
+		if(c == C_DARK) c = C_BLACK;
+		if(c == C_LIGHT) c = C_WHITE;
+		dpixel(x+dx, y+dy, c);
+	}
+}
+
+void img_render_vram_gray(img_t img, int x, int y)
+{
+	img_pixel_t *px = img.pixels;
+
+	for(int dy = 0; dy < img.height; dy++, px += img.stride)
+	for(int dx = 0; dx < img.width; dx++)
+	{
+		gpixel(x+dx, y+dy, px[dx]);
 	}
 }
 #endif /* FX9860G */