Merge pull request #39 from dschweinbenz/feature/leftMargin

Add functionality to set left margin using GS command

Author: dohooo

.changeset/strange-lies-attack.md

@@ -0,0 +1,5 @@
+---
+"@node-escpos/core": minor
+---
+
+Added function to set left margin using GS command

packages/core/src/index.ts

@@ -162,6 +162,23 @@ export class Printer<AdapterCloseArgs extends []> extends EventEmitter {
     return this;
   }
 
+  /**
+   * Set left margin using GS command
+   * @param  {[String]} size
+   * @return {[Printer]} printer  [the escpos printer instance]
+   */
+  setMarginLeft(size: number): Printer<AdapterCloseArgs> {
+    if (size > 65535) {
+      throw new Error("Max margin range exceeded");
+    }
+    // 1D 4C nL nH
+    this.buffer.write(_.GS);
+    this.buffer.write("\x4C");
+    const nL_nH = utils.intLowHighHex(size, 2);
+    this.buffer.write(Buffer.from(nL_nH, 'hex'));
+    return this;
+  }
+
   /**
    * Fix right margin
    * @param  {[String]} size

packages/core/src/utils.ts

@@ -40,3 +40,27 @@ export type AnyCase<T extends string> = Uppercase<T> | Lowercase<T>;
 export function isKey<T extends {} | []>(key: string | number | symbol, of: T): key is keyof T {
   return key in of;
 }
+
+/**
+ * Function to encode a number as hex in format low to high values
+ * @param {[Number]} input 
+ * @param {[Number]} length of hex couples (0x01 0x00 ...)
+ * @returns {[string]} hex value low-high order
+ */
+export function intLowHighHex(input: number, length: number = 1): string {
+  if (input < 0 || input % 1 !== 0) {
+    throw new Error('Input must be greater or equal than 0');
+  } else if (length < 0) {
+    throw new Error('Length muste be greater than 0');
+  }
+  let ret = ''
+  for (let i = 0; i < length; i++) {
+    let value = (input % 256).toString(16).toUpperCase();
+    if (value === '0' || value.length % 2 !== 0) {
+      value = `0${value}`;
+    }
+    ret += value;
+    input = Math.floor(input / 256);
+  }
+  return ret;
+}