From 915dd4b023d0826166d4887100dbed64d46821a9 Mon Sep 17 00:00:00 2001
From: Andreas Baumann <mail@andreasbaumann.cc>
Date: Fri, 30 Jun 2017 15:02:26 +0200
Subject: playing with Z buffering in VGA driver

---
 src/drivers/video/vga.c | 21 +++++++++++++++++----
 src/drivers/video/vga.h |  9 +++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

(limited to 'src/drivers')

diff --git a/src/drivers/video/vga.c b/src/drivers/video/vga.c
index 9d540af..bcd4366 100644
--- a/src/drivers/video/vga.c
+++ b/src/drivers/video/vga.c
@@ -253,7 +253,7 @@ bool vga_set_mode( vga_t *vga, const vga_mode_t mode )
 	vga->mode = mode;
 	vga->mode.segment = get_frame_buffer_segment( vga );
 
-	vga->use_z_buffer = false;
+	vga_use_z_buffer( vga, false );
 
 	return true;
 }
@@ -317,7 +317,7 @@ void vga_set_pixel( vga_t *vga, const int x, const int y, const vga_color_t colo
 
 	uint8_t color_idx = get_color_index( color );
 
-	uint8_t *addr = vga->mode.segment + vga->mode.x * y + x;
+	uint8_t *addr = vga->base_addr + vga->mode.x * y + x;
 
 	*addr = color_idx;
 }	
@@ -337,14 +337,14 @@ void vga_draw_rectangle( vga_t *vga, const int x, const int y, const int w, cons
 	uint8_t color_idx = get_color_index( color );
 
 	for( int yy = y; yy < y + h; yy++ ) {
-		uint8_t *addr = vga->mode.segment + vga->mode.x * yy + x;
+		uint8_t *addr = vga->base_addr + vga->mode.x * yy + x;
 		memset( addr, color_idx, w );
 	}
 }
 
 void vga_clear_screen( vga_t *vga, const vga_color_t color )
 {
-	memset( vga->mode.segment, get_color_index( color ),
+	memset( vga->base_addr, get_color_index( color ),
 		vga->mode.x * vga->mode.y );
 }
 
@@ -385,6 +385,19 @@ void vga_wait_for_retrace( vga_t *vga )
 void vga_use_z_buffer( vga_t *vga, bool use )
 {
 	vga->use_z_buffer = use;
+
+	if( vga->use_z_buffer ) {
+		vga->base_addr = &vga->zbuffer[0];
+	} else {
+		vga->base_addr = vga->mode.segment;
+	}
 }
 
+void vga_refresh( vga_t *vga )
+{
+	if( vga->use_z_buffer ) {
+		vga_wait_for_retrace( vga );
+		memcpy( vga->mode.segment, vga->zbuffer, 65535 );
+	}
+}
 
diff --git a/src/drivers/video/vga.h b/src/drivers/video/vga.h
index 0f55f74..d15a55d 100644
--- a/src/drivers/video/vga.h
+++ b/src/drivers/video/vga.h
@@ -43,6 +43,14 @@ typedef struct {
 	vga_mode_t mode;
 	void *context;
 	bool use_z_buffer;
+	// TODO: the Z-buffer should actually be allocated dynamically
+	// depending on the current mode, for now it's a static buffer
+	// able to store the biggest resolution, being planar
+	// 320x200x8 aka 64k
+	uint8_t zbuffer[65535];
+	// stores either the address to the beginning of the segment
+	// (real mapped I/O memory or the beginning of the Z buffer
+	uint8_t *base_addr;
 } vga_t;
 
 typedef struct {
@@ -83,5 +91,6 @@ void vga_clear_screen( vga_t *vga, const vga_color_t color );
 void vga_draw_char( vga_t *vga, const unsigned char c, const int x, const int y, const vga_color_t background, const vga_color_t foreground );
 void vga_wait_for_retrace( vga_t *vga );
 void vga_use_z_buffer( vga_t *vga, bool use );
+void vga_refresh( vga_t *vga );
 
 #endif // VGA_H
-- 
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