don't do full render when zooming happens in viewport rather than

offscreen canvas
don't do clearRect on renderChunk (Chrome shouldn't have the flickering
issue anymore)

src/core/Markdown.js

@@ -65,10 +65,15 @@ export default class MarkdownParser {
 
   /*
    * parses Articles (contains paragraphs, code-blocks, numeration, etc.)
-   * returns when encountering heading of level or lower (iter is at # position)
+   * @param text string of text
+   * @param start number of position in text where to start
+   * @param level the number of heading levels we are in
+   * @param indent ndentation that should be considered
+   * returns when encountering heading of <= level (iter is at # position)
    *   or heading-cancel with three spaces (iter is past newlines)
+   *   or ident is smaller than given
    */
-  parseArticle(text: string, start: number, level = 0) {
+  parseArticle(text: string, start: number, level = 0, indent = 0) {
     let iter = start;
     const mdArray = [];
     let paraStart = iter;
@@ -116,6 +121,11 @@ export default class MarkdownParser {
     return [mdArray, iter];
   }
 
+  parseList(text: string, start: number) {
+    const iter = start;
+    const mdArray = [];
+  }
+
   /*
    * parse Code Block
    * start is first character after the initializing ```

src/store/rendererHook.js

@@ -12,17 +12,32 @@ import {
 export default (store) => (next) => (action) => {
   const { type } = action;
 
-  if (type === 'SET_HISTORICAL_TIME') {
-    const state = store.getState();
-    const renderer = getRenderer();
-    const {
-      historicalDate: oldDate,
-      historicalTime: oldTime,
-    } = state.canvas;
-    renderer.updateOldHistoricalTime(
-      oldDate,
-      oldTime,
-    );
+  let prevScale = null;
+
+  switch (type) {
+    case 'TOGGLE_HISTORICAL_VIEW':
+    case 'SET_SCALE': {
+      const state = store.getState();
+      prevScale = state.canvas.viewscale;
+      break;
+    }
+
+    case 'SET_HISTORICAL_TIME': {
+      const state = store.getState();
+      const renderer = getRenderer();
+      const {
+        historicalDate: oldDate,
+        historicalTime: oldTime,
+      } = state.canvas;
+      renderer.updateOldHistoricalTime(
+        oldDate,
+        oldTime,
+      );
+      break;
+    }
+
+    default:
+      // nothing
   }
 
   // executed after reducers
@@ -78,7 +93,7 @@ export default (store) => (next) => (action) => {
     case 'TOGGLE_HISTORICAL_VIEW':
     case 'SET_SCALE': {
       const renderer = getRenderer();
-      renderer.updateScale(state);
+      renderer.updateScale(state, prevScale);
       break;
     }
 

src/ui/Renderer2D.js

@@ -176,6 +176,7 @@ class Renderer {
 
   updateScale(
     state,
+    prevScale = null,
   ) {
     const {
       viewscale,
@@ -196,7 +197,12 @@ class Renderer {
     this.tiledZoom = tiledZoom;
     this.relScale = relScale;
     this.updateView(state);
-    this.forceNextRender = true;
+    if (prevScale === null
+      || viewscale < SCALE_THREASHOLD || prevScale < SCALE_THREASHOLD) {
+      this.forceNextRender = true;
+    } else {
+      this.forceNextSubrender = true;
+    }
   }
 
   updateView(state) {
@@ -307,9 +313,6 @@ class Renderer {
     } = state.canvas;
 
     let { relScale } = this;
-    // clear rect is just needed for Google Chrome, else it would flash
-    // regularly
-    context.clearRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
 
     // Disable smoothing
     // making it dependent on the scale is needed for Google Chrome, else
@@ -544,9 +547,6 @@ class Renderer {
       historicalCanvasSize,
     } = state.canvas;
 
-
-    // clear rect is just needed for Google Chrome, else it would flash
-    context.clearRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
     // Disable smoothing
     // making it dependent on the scale is needed for Google Chrome, else
     // scale <1 would look shit