Mirrored rendering for negative dimensions with rect().

ellipse() and arc() use absolute values

src/core/helpers.js

@@ -16,14 +16,12 @@ function modeAdjust(a, b, c, d, mode) {
   if (mode === constants.CORNER) {
 
     // CORNER mode already corresponds to a bounding box (top-left corner, width, height).
-    // Negative dimensions (width and/or height) result in 'flipping' the shape.
-    if (c < 0) { c = -c; a -= c;  } // Negative width: Move shape to the left (flip left)
-    if (d < 0) { d = -d; b -= d;  } // Negative height: Move shape up (flip up)
+    // For negative widhts or heights, the absolute value is used.
     bbox = {
       x: a,
       y: b,
-      w: c,
-      h: d
+      w: Math.abs(c),
+      h: Math.abs(d)
     };
 
   } else if (mode === constants.CORNERS) {

src/core/shape/2d_primitives.js

@@ -1339,6 +1339,15 @@ p5.prototype._renderRect = function() {
       this._renderer._rectMode
     );
 
+    // For the default rectMode (CORNER), restore a possible negative width/height
+    // removed by modeAdjust(). This results in flipped/mirrored rendering,
+    // which is especially noticable when using WEGBL rendering and texture().
+    // Note that this behavior only applies to rect(), NOT to ellipse() and arc().
+    if (this._renderer._rectMode === constants.CORNER) {
+      vals.w = arguments[2];
+      vals.h = arguments[3];
+    }
+
     const args = [vals.x, vals.y, vals.w, vals.h];
     // append the additional arguments (either cornder radii, or
     // segment details) to the argument list

test/unit/visual/cases/shape_modes.js

@@ -17,10 +17,12 @@ function shapeCorners(p5, shape, mode, x1, y1, x2, y2) {
     // Don't use abs(), so we get negative values as well
     let w = x2 - x1; // w
     let h = y2 - y1; // h
-    // With mode CORNER, negative widths/heights result in mirrored/flipped shapes
-    // In this case, adjust position so the shape is in line with the other cases
-    if (w < 0) { x += (-w); } // Move right
-    if (h < 0) { y += (-h); } // Move down
+    // With mode CORNER, rects with negative widths/heights result in mirrored/flipped rendering
+    // In this case, adjust position so the rect is in line with the other cases
+    if (shape === 'rect') {
+      if (w < 0) { x += (-w); } // Move right
+      if (h < 0) { y += (-h); } // Move down
+    }
     x1 = x; y1 = y; x2 = w; y2 = h;
   } else if (mode === p5.CENTER) {
     // Find center
@@ -124,10 +126,11 @@ visualSuite('Shape Modes', function(...args) {
 
   /*
     An extra test suite specific to shape mode CORNER and negative dimensions.
-    Negative width should result in the shape flipped horizontally (to the left).
-    Negative height should result in the shape flipped vertically (up).
+    For rect, negative widths/heights result in flipped rendering (horizontally/vertically)
+    For ellipse and arc, using negative widths/heights has no effect (the absolute value is used)
   */
   visualSuite('Negative dimensions', function() {
+    // Negative widths/height result in flipped rects.
     visualTest('rect', function(p5, screenshot) {
       p5.createCanvas(50, 50);
       p5.translate(p5.width/2, p5.height/2);
@@ -141,6 +144,8 @@ visualSuite('Shape Modes', function(...args) {
       p5.rect(0, 0, -20, -10);
       screenshot();
     });
+    // Since negative widths/heights are used with their absolute value,
+    // ellipses are drawn on top of each other, blue one last
     visualTest('ellipse', function(p5, screenshot) {
       p5.createCanvas(50, 50);
       p5.translate(p5.width/2, p5.height/2);
@@ -154,6 +159,8 @@ visualSuite('Shape Modes', function(...args) {
       p5.ellipse(0, 0, -20, -10);
       screenshot();
     });
+    // Since negative widths/heights are used with their absolute value,
+    // arcs are drawn on top of each other, blue one last.
     visualTest('arc', function(p5, screenshot) {
       p5.createCanvas(50, 50);
       p5.translate(p5.width/2, p5.height/2);