Add `er.useMaxWidth` config option

This restores the option of rendering an ERD with an absolute width,
which is consistent with the approach taken with the other diagram
types.

This logic was lost in #1324, which was probably just a small oversight:

9199546dca (diff-7c38d27acbe0676d923bf19283671616L397-L409)

The option defaults to true for backwards compatibility.

docs/Setup.md

@@ -705,9 +705,21 @@ T = top, B = bottom, L = left, and R = right.
 | --------- | ------------------- | ------- | -------- | ------------------ |
 | fontSize  | Font Size in pixels | Integer |          | Any Positive Value |
 
-**Notes:**Font size (expressed as an integer representing a number of  pixels)
+**Notes:**Font size (expressed as an integer representing a number of pixels)
 **Default value: 12 **
 
+### useMaxWidth
+
+| Parameter   | Description | Type    | Required | Values      |
+| ----------- | ----------- | ------- | -------- | ----------- |
+| useMaxWidth | See Notes   | Boolean | Required | true, false |
+
+**Notes:**
+When this flag is set to true, the diagram width is locked to 100% and
+scaled based on available space. If set to false, the diagram reserves its
+absolute width.
+**Default value: true**.
+
 ## render
 
 Function that renders an svg with a graph from a chart definition. Usage example below.

src/config.js

@@ -801,10 +801,23 @@ const config = {
      *| --- | --- | --- | --- | --- |
      *| fontSize| Font Size in pixels| Integer |  | Any Positive Value |
      *
-     ***Notes:**Font size (expressed as an integer representing a number of  pixels)
+     ***Notes:**Font size (expressed as an integer representing a number of pixels)
      ***Default value: 12 **
      */
-    fontSize: 12
+    fontSize: 12,
+
+    /**
+     *| Parameter | Description |Type | Required | Values|
+     *| --- | --- | --- | --- | --- |
+     *| useMaxWidth | See Notes | Boolean | Required | true, false |
+     *
+     ***Notes:**
+     *When this flag is set to true, the diagram width is locked to 100% and
+     *scaled based on available space. If set to false, the diagram reserves its
+     *absolute width.
+     ***Default value: true**.
+     */
+    useMaxWidth: true
   }
 };
 config.class.arrowMarkerAbsolute = config.arrowMarkerAbsolute;

src/diagrams/er/erRenderer.js

@@ -339,9 +339,14 @@ export const draw = function(text, id) {
   const width = svgBounds.width + padding * 2;
   const height = svgBounds.height + padding * 2;
 
-  svg.attr('height', height);
-  svg.attr('width', '100%');
-  svg.attr('style', `max-width: ${width}px;`);
+  if (conf.useMaxWidth) {
+    svg.attr('width', '100%');
+    svg.attr('style', `max-width: ${width}px;`);
+  } else {
+    svg.attr('height', height);
+    svg.attr('width', width);
+  }
+
   svg.attr('viewBox', `${svgBounds.x - padding} ${svgBounds.y - padding} ${width} ${height}`);
 }; // draw