implemented viewport

.gitignore

@@ -2,3 +2,4 @@ bin
 *.dylib
 .DS_Store
 src/src
+scratch

src/main.odin

@@ -1,5 +1,5 @@
 /*
-- TODO implement movement up and down by paragraph
+- DONE implement movement up and down by paragraph
 - TODO implement scrolling/viewport
 - TODO implement deletion by word
 - TODO implement selection
@@ -27,18 +27,27 @@ read_file :: proc(path: string) -> (string, bool) {
 	return string(content), success
 }
 
+Viewport :: struct {
+	start: int,
+	end: int,
+}
+
 Cursor :: struct {
 	line: int,
 	char: int,
 }
 
+window_width := 800
+window_height := 600
 font_size: f32 = 20.0
 text_height: f32
 cursor: Cursor
 lines: [dynamic][dynamic]u8
+viewport_size := window_height / int(font_size)
+viewport := Viewport{start = 0, end = viewport_size}
 
 main :: proc() {
-	r.InitWindow(800, 600, "odit")
+	r.InitWindow(i32(window_width), i32(window_height), "odit")
 	r.SetTargetFPS(60)
 	font := r.LoadFont("/Users/grant/Library/Fonts/BerkeleyMono-Regular.otf")
 	r.GuiSetFont(font)
@@ -139,7 +148,7 @@ main :: proc() {
 				}
 			}
 
-			cursor.line = min(preferred_line, len(lines))
+			cursor.line = min(preferred_line, len(lines) - 1)
 			if len(current_line()) < cursor.char {
 				cursor.char = len(current_line())
 			}
@@ -186,10 +195,24 @@ main :: proc() {
 			}
 		}
 
+		cursor_padding := 3
+		// move viewport up
+		if cursor.line < viewport.start + cursor_padding {
+			diff := (cursor.line - viewport.start) - cursor_padding
+			viewport.start = min(max(0, viewport.start + diff), len(lines) - viewport_size)
+			viewport.end = min(max(viewport_size, viewport.end + diff), len(lines))
+		}
+		// move viewport down
+		if viewport.end - cursor_padding < cursor.line {
+			diff := cursor.line - (viewport.end - cursor_padding)
+			viewport.start = min(max(0, viewport.start + diff), len(lines) - viewport_size)
+			viewport.end = min(max(viewport_size, viewport.end + diff), len(lines))
+		}
+
 		r.BeginDrawing()
 		r.ClearBackground(r.BLACK)
 
-		for &line, line_index in lines {
+		for &line, line_index in lines[viewport.start:viewport.end] {
 			if cap(line) == 0 {
 				reserve(&line, 1)
 			}
@@ -216,9 +239,9 @@ main :: proc() {
 
 render_cursor :: proc(cursor: ^Cursor) {
 	x := cursor.char * int(font_size / 2)
-	y := i32(font_size) * i32(cursor.line)
-	r.DrawLine(i32(x), y, i32(x), y + i32(text_height), r.WHITE)
-	r.DrawLine(i32(x) + 1, y, i32(x) + 1, y + i32(text_height), r.WHITE)
+	y := i32(font_size) * i32(cursor.line - viewport.start)
+	r.DrawLine(i32(x), y, i32(x), y + i32(font_size), r.WHITE)
+	r.DrawLine(i32(x) + 1, y, i32(x) + 1, y + i32(font_size), r.WHITE)
 }
 
 current_line :: proc() -> ^[dynamic]u8 {