Added support for backspace merge. (#11)

src/cmd_ops.c

@@ -96,6 +96,27 @@ static void scroll_down_from_top(screen* scr, text_buffer* buf, uint8_t ch) {
     }
     vdp_cursor_tab(scr->currY_, scr->currX_);
     scr_show_cursor_ch(scr, ch);
+
+    vdp_cursor_tab(scr->currY_, 0);
+    int psz = 0;
+    uint8_t* prefix = tb_prefix(buf, &psz);
+    int i = 0;
+    int pad = buf->x_ - scr->currX_;
+    if (pad < 0) {
+        pad = 0;
+    }
+    for (; i < scr->currX_; i++) {
+        putch(prefix[i+pad]);
+    }
+
+    int sz = 0;
+    uint8_t* suffix = tb_suffix(buf, &sz);
+    for (int j = 0; j < sz && i < scr->cols_; i++, j++) {
+        putch(suffix[j]);
+    }
+    vdp_cursor_tab(scr->currY_, scr->currX_);
+    scr_show_cursor_ch(scr, ch);
+
 }
 
 static void scroll_up_from_top(screen* scr, text_buffer* buf, uint8_t ch) {
@@ -180,8 +201,27 @@ void cmd_del(screen* scr, text_buffer* buf) {
     scr_del(scr, suffix, sz);
 }
 
+static void cmd_bksp_merge(screen* scr, text_buffer* buf) {
+    if (!tb_bksp_merge(buf)) {
+        return;
+    }
+    uint8_t ch = tb_peek(buf);
+    if (scr->currY_ > scr->topY_) {
+        scr->currY_--;
+    }
+    if (buf->x_ > scr->cols_-1) {
+        scr->currX_ = scr->cols_-1;
+    } else {
+        scr->currX_ = buf->x_;
+    }
+    scroll_down_from_top(scr, buf, ch);
+}
+
 void cmd_bksp(screen* scr, text_buffer* buf) {
     if (tb_bol(buf)) {
+        if (tb_ypos(buf) > 1) {
+            cmd_bksp_merge(scr, buf);
+        }
         return;
     }
 

src/line_buffer.c

@@ -128,6 +128,21 @@ bool lb_merge_next(line_buffer* lb) {
     return true;
 }
 
+int lb_merge_prev(line_buffer* lb) {
+    if (lb->curr_ == lb->buf_) {
+        return -1;
+    }
+
+    int curr = *lb->curr_;
+    lb->curr_--;
+    (*lb->curr_) -= 2;
+    int next = *lb->curr_;
+    (*lb->curr_) += curr;
+
+    return next;
+}
+
+
 int lb_copy(line_buffer* lb, uint8_t* buf, int size) {
     const int prefix = lb->curr_ - lb->buf_+1;
     int used;

src/line_buffer.h

@@ -50,6 +50,7 @@ bool lb_down(line_buffer* lb);
 bool lb_new(line_buffer* lb, int size);
 bool lb_del(line_buffer* lb);
 bool lb_merge_next(line_buffer* lb);
+int lb_merge_prev(line_buffer* lb);
 
 int lb_copy(line_buffer* cb, uint8_t* buf, int size);
 

src/text_buffer.c

@@ -133,6 +133,17 @@ bool tb_del_merge(text_buffer* tb) {
     return true;
 }
 
+bool tb_bksp_merge(text_buffer* tb) {
+    if (!tb_bol(tb) || tb_ypos(tb) == 1) {
+        return false;
+    }
+    cb_bksp(&tb->cb_);
+    cb_bksp(&tb->cb_);
+
+    tb->x_ = lb_merge_prev(&tb->lb_);
+    return true;
+}
+
 
 // Cursor ops.
 uint8_t tb_next(text_buffer* tb) {

src/text_buffer.h

@@ -47,6 +47,7 @@ bool tb_bksp(text_buffer* tb);
 bool tb_newline(text_buffer* tb);
 bool tb_del_line(text_buffer* tb);
 bool tb_del_merge(text_buffer* tb);
+bool tb_bksp_merge(text_buffer* tb);
 
 // Cursor ops.
 uint8_t tb_next(text_buffer* tb);