From d1b939414c3dbc0f82ccfbaf17985ec7dddc6062 Mon Sep 17 00:00:00 2001
From: Lawrence Kesteloot <lk@teamten.com>
Date: Fri, 3 Aug 2018 18:57:30 -0700
Subject: [PATCH] Add GR and TEXT commands.

---
 main.c    | 10 ++++++++++
 runtime.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
 runtime.h |  3 +++
 3 files changed, 60 insertions(+), 3 deletions(-)

diff --git a/main.c b/main.c
index f62dc25..611040c 100644
--- a/main.c
+++ b/main.c
@@ -45,6 +45,8 @@ uint8_t title_length = 9;
 #define T_GOTO 0x90
 #define T_IF 0x91
 #define T_THEN 0x92
+#define T_GR 0x93
+#define T_TEXT 0x94
 
 // Operators. These encode both the operator (high nybble) and the precedence
 // (low nybble). Lower precedence has a lower low nybble value. For example,
@@ -113,6 +115,8 @@ static uint8_t *TOKEN[] = {
     "GOTO",
     "IF",
     "THEN",
+    "GR",
+    "TEXT",
 };
 static int16_t TOKEN_COUNT = sizeof(TOKEN)/sizeof(TOKEN[0]);
 
@@ -761,6 +765,12 @@ static void compile_buffer(uint8_t *buffer, uint16_t line_number) {
                 g_compiled_length = saved_compiled_length;
                 error = 1;
             }
+        } else if (*s == T_GR) {
+            s += 1;
+            add_call(gr_statement);
+        } else if (*s == T_TEXT) {
+            s += 1;
+            add_call(text_statement);
         } else {
             error = 1;
         }
diff --git a/runtime.c b/runtime.c
index 9f6ed92..73ab6ef 100644
--- a/runtime.c
+++ b/runtime.c
@@ -6,6 +6,8 @@
 #define SCREEN_HEIGHT 24
 #define SCREEN_WIDTH 40
 #define SCREEN_STRIDE (3*SCREEN_WIDTH + 8)
+#define MIXED_TEXT_HEIGHT 4
+#define MIXED_GRAPHICS_HEIGHT (SCREEN_HEIGHT - MIXED_TEXT_HEIGHT)
 #define CLEAR_CHAR (' ' | 0x80)
 
 // Location of cursor in logical screen space.
@@ -16,6 +18,9 @@ uint16_t g_showing_cursor = 0;
 // Character at the cursor location.
 uint8_t g_cursor_ch = 0;
 
+// Whether in low-res graphics mode.
+uint8_t g_gr_mode = 0;
+
 // List of variable names, two bytes each, in the same order they are
 // in the zero page (starting at FIRST_VARIABLE). Two nuls means an unused
 // slot. One-letter variable names have a nul for the second character.
@@ -103,17 +108,17 @@ void home(void) {
  */
 static void scroll_up(void) {
     int i;
+    int first_line = g_gr_mode ? MIXED_GRAPHICS_HEIGHT : 0;
     uint8_t *previous_line = 0;
 
-    for (i = 0; i < SCREEN_HEIGHT; i++) {
+    for (i = first_line; i < SCREEN_HEIGHT; i++) {
         uint8_t *this_line = screen_pos(0, i);
-        if (i > 0) {
+        if (i > first_line) {
             memmove(previous_line, this_line, SCREEN_WIDTH);
         }
         previous_line = this_line;
     }
 
-    // This is provided by cc65:
     memset(previous_line, CLEAR_CHAR, SCREEN_WIDTH);
 }
 
@@ -206,3 +211,42 @@ void syntax_error_in_line(uint16_t line_number) {
 
     // No linefeed, assume prompt will do it.
 }
+
+/**
+ * Switch to graphics mode.
+ */
+void gr_statement(void) {
+    int i;
+    uint8_t *p = (uint8_t *) 49235U;
+
+    hide_cursor();
+
+    // Mixed text and lo-res graphics mode.
+    *p = 0;
+
+    // Clear the graphics area.
+    for (i = 0; i < MIXED_GRAPHICS_HEIGHT; i++) {
+        memset(screen_pos(0, i), 0, SCREEN_WIDTH);
+    }
+
+    // Move the cursor to the text window.
+    if (g_cursor_y < MIXED_GRAPHICS_HEIGHT) {
+        move_cursor(0, MIXED_GRAPHICS_HEIGHT);
+    }
+
+    g_gr_mode = 1;
+}
+
+/**
+ * Switch to text mode.
+ */
+void text_statement(void) {
+    uint8_t *p = (uint8_t *) 49233U;
+
+    hide_cursor();
+
+    // Mixed text and lo-res graphics mode.
+    *p = 0;
+
+    g_gr_mode = 0;
+}
diff --git a/runtime.h b/runtime.h
index 5b72e04..66c186c 100644
--- a/runtime.h
+++ b/runtime.h
@@ -36,4 +36,7 @@ void print_newline(void);
 void syntax_error(void);
 void syntax_error_in_line(uint16_t line_number);
 
+void gr_statement(void);
+void text_statement(void);
+
 #endif // __RUNTIME_H__