From 7f8f7f3d6f42e6ef9761881112617bd70ebe7e9d Mon Sep 17 00:00:00 2001
From: Pavel Tisnovsky <ptisnovs@redhat.com>
Date: Thu, 11 Jul 2024 15:45:47 +0200
Subject: [PATCH] Character heights

---
 pc-dos/cga_text_mode_char_height.asm | 76 ++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 pc-dos/cga_text_mode_char_height.asm

diff --git a/pc-dos/cga_text_mode_char_height.asm b/pc-dos/cga_text_mode_char_height.asm
new file mode 100644
index 00000000..a245c9db
--- /dev/null
+++ b/pc-dos/cga_text_mode_char_height.asm
@@ -0,0 +1,76 @@
+; Textovy rezim karty CGA.
+;
+; preklad pomoci:
+;     nasm -f bin -o gfx_text.com gfx_cga_text_mode_1.asm
+;
+; nebo pouze:
+;     nasm -o gfx_text.com gfx_cga_text_mode_1.asm
+
+
+;-----------------------------------------------------------------------------
+
+; ukonceni procesu a navrat do DOSu
+%macro exit 0
+        mov     ah, 0x4c
+        int     0x21
+%endmacro
+
+; vyprazdneni bufferu klavesnice a cekani na klavesu
+%macro wait_key 0
+        xor     ax, ax
+        int     0x16
+%endmacro
+
+; nastaveni grafickeho rezimu
+%macro gfx_mode 1
+        mov     ah, 0
+        mov     al, %1
+        int     0x10
+%endmacro
+
+; zmena vysky znaku
+%macro character_height 1
+        mov dx, 0x3d4
+        mov al, 0x09    ; ridici registr (CRTC)
+        out dx, al
+        mov dx, 0x3d5
+        mov al, %1      ; nastavit pozadovanou vysku znaku
+        out dx, al
+%endmacro
+
+;-----------------------------------------------------------------------------
+org  0x100        ; zacatek kodu pro programy typu COM (vzdy se zacina na 256)
+
+start:
+        gfx_mode 3      ; nastaveni textoveho rezimu 80x25 znaku
+
+        mov ax, 0xb800
+        mov es, ax
+        mov di, 0       ; nyni ES:DI obsahuje adresu prvniho znaku ve video RAM
+
+        mov cx, 40*25   ; pocet zapisovanych znaku
+        mov al, 0       ; kod zapisovaneho znaku
+opak:
+        stosb           ; zapis znaku + atributu
+        stosb
+        inc al          ; dalsi znak/atribut
+        loop opak       ; opakujeme CX-krat
+
+        wait_key
+
+        mov dx, 0x3d8   ; port s rizenim graficke palety
+        mov al, 0x18    ; pozadi neblika, meni se intenzita
+        out dx, al      ; pres port 0x3d9
+
+        wait_key
+
+        character_height 6
+        wait_key
+
+        character_height 1
+        wait_key
+
+        character_height 0
+        wait_key
+
+        exit