Tests: set a minimum number of accepted different pixels in `ImageCom…

…parator`

It applies when the allowance is greater than zero but less than 1%.

echosvg-test/src/test/java/io/sf/carte/echosvg/test/image/ImageComparator.java

@@ -85,6 +85,28 @@ public class ImageComparator {
 	 */
 	private static final int diffPixelFactor = 10;
 
+	private static int minDiffPixelsForNonzeroAllowance = 30;
+
+	/**
+	 * Set the bare minimum number of accepted different pixels, to apply when the
+	 * allowance is greater than zero but less than 1%, and when it is smaller than
+	 * the smallest of the image sides.
+	 * <p>
+	 * Applies independently to pixels above and below the threshold.
+	 * </p>
+	 * <p>
+	 * This is useful for small images. Default value is 30.
+	 * </p>
+	 * 
+	 * @param minDiffPixelsForNonzeroAllowance a positive integer.
+	 */
+	public static void setMinDiffPixelsForNonzeroAllowance(int minDiffPixelsForNonzeroAllowance) {
+		if (minDiffPixelsForNonzeroAllowance < 0) {
+			throw new IllegalArgumentException("Number of pixels must be at least 0.");
+		}
+		ImageComparator.minDiffPixelsForNonzeroAllowance = minDiffPixelsForNonzeroAllowance;
+	}
+
 	/**
 	 * Compare two images, allowing a percentage of different pixels according to a
 	 * threshold value.
@@ -151,8 +173,9 @@ public static short compareImages(BufferedImage ref, BufferedImage can, int pixe
 
 		final int numBands = ref.getSampleModel().getNumBands();
 		final float numpxFrac = w * h * numBands * 0.01f;
-		final int maxDiffPx = Math.round(numpxFrac * allowedPercentOverThreshold);
-		final int maxDiffPxBelow = Math.round(numpxFrac * allowedPercentBelowThreshold);
+		final int maxDiffPx = computeMaxDiffPixels(numpxFrac, allowedPercentOverThreshold, w, h);
+		final int maxDiffPxBelow = computeMaxDiffPixels(numpxFrac, allowedPercentBelowThreshold, w,
+				h);
 
 		WritableRaster refWR = ref.getRaster();
 		WritableRaster canWR = can.getRaster();
@@ -217,6 +240,29 @@ public static short compareImages(BufferedImage ref, BufferedImage can, int pixe
 		return result;
 	}
 
+	private static int computeMaxDiffPixels(float numpxFrac, float allowedPercent, int width,
+			int height) {
+		int maxDiffPx;
+
+		if (allowedPercent == 0f) {
+			maxDiffPx = 0;
+		} else {
+			maxDiffPx = Math.round(numpxFrac * allowedPercent);
+			// If allowedPercent is small but nonzero, maybe there are too few accepted misses.
+			if (maxDiffPx < minDiffPixelsForNonzeroAllowance && allowedPercent < 1f) {
+				// We want to accept at most the number of pixels in a side, minus one.
+				int minDiff = Math.min(width, height) - 1;
+				minDiff = Math.min(minDiff, minDiffPixelsForNonzeroAllowance);
+				if (maxDiffPx < minDiff) {
+					// Allow at least minDiff pixels for (0 < allowedPercent < 1).
+					maxDiffPx = minDiff;
+				}
+			}
+		}
+
+		return maxDiffPx;
+	}
+
 	/**
 	 * Compare a candidate image to a reference, taking into account one or more
 	 * possible variations.
@@ -288,8 +334,9 @@ public static short compareVariantImages(BufferedImage ref, BufferedImage can, i
 
 		final int numBands = ref.getSampleModel().getNumBands();
 		final float numpxFrac = w * h * numBands * 0.01f;
-		final int maxDiffPx = Math.round(numpxFrac * allowedPercentOverThreshold);
-		final int maxDiffPxBelow = Math.round(numpxFrac * allowedPercentBelowThreshold);
+		final int maxDiffPx = computeMaxDiffPixels(numpxFrac, allowedPercentOverThreshold, w, h);
+		final int maxDiffPxBelow = computeMaxDiffPixels(numpxFrac, allowedPercentBelowThreshold, w,
+				h);
 
 		WritableRaster refWR = ref.getRaster();
 		WritableRaster canWR = can.getRaster();
@@ -521,6 +568,42 @@ public interface ImageVariants {
 		BufferedImage getVariantImage(int index);
 	}
 
+	public static String getResultDescription(short code) {
+		String desc;
+		switch (code) {
+		case MATCH:
+			desc = "Match";
+			break;
+		case DIFFERENT_SIZES:
+			desc = "The images have different sizes";
+			break;
+		case DIFFERENT_TRANSPARENCIES:
+			desc = "The images have different sizes";
+			break;
+		case DIFFERENT_TYPES:
+			desc = "The images are of different types";
+			break;
+		case DIFFERENT_COLOR_SPACES:
+			desc = "The images have different color spaces";
+			break;
+		case DIFFERENT_PIXELS_BELOW_THRESHOLD:
+			desc = "The images have have too many below-threshold different pixels";
+			break;
+		case DIFFERENT_PIXELS_OVER_THRESHOLD:
+			desc = "The images have have too many over-threshold different pixels";
+			break;
+		case NO_VARIANTS:
+			desc = "A variant comparison was executed but no variants were found";
+			break;
+		case VARIANT_ERROR:
+			desc = "At least one of the image variants is wrong (wrong size, etc)";
+			break;
+		default:
+			desc = "unknown code";
+		}
+		return desc;
+	}
+
 	/**
 	 * Creates an image comparing the two given images, one on each side.
 	 * 

echosvg-test/src/test/java/io/sf/carte/echosvg/test/svg/AbstractRenderingAccuracyTest.java

@@ -430,7 +430,8 @@ public void runTest(float allowedPercentBelowThreshold, float allowedPercentOver
 			tmpFile.delete();
 		}
 
-		fail("Rendering not accurate [code " + result + "], see generated images: " + diffFile.getAbsolutePath() + ", "
+		fail("Rendering not accurate [" + ImageComparator.getResultDescription(result)
+				+ "], see generated images: " + diffFile.getAbsolutePath() + ", "
 				+ cmpFile.getAbsolutePath());
 	}
 

echosvg-test/src/test/java/io/sf/carte/echosvg/test/svg/ImageCompareTest.java

@@ -148,8 +148,8 @@ public String compare(float allowedPercentBelowThreshold, float allowedPercentOv
 		File tmpDiff = imageToFile(diff, IMAGE_TYPE_DIFFERENCE);
 		File tmpCmp = imageToFile(cmp, IMAGE_TYPE_COMPARISON);
 
-		return "Images are different [code " + result + "]. Comp: " + tmpCmp.getAbsolutePath() + " diff: "
-				+ tmpDiff.getAbsolutePath();
+		return "Images are different [" + ImageComparator.getResultDescription(result) + "]. Comp: "
+				+ tmpCmp.getAbsolutePath() + " diff: " + tmpDiff.getAbsolutePath();
 
 	}
 

echosvg-test/src/test/java/io/sf/carte/echosvg/test/svg/SamplesCanvgRenderingTest.java

@@ -1308,17 +1308,14 @@ public void testSwz721b_webfont() throws TranscoderException, IOException {
 		testNV("samples/canvg/swz721b-webfont.svg");
 	}
 
-	/*
-	 * Put larger thresholds due to smaller file sizes.
-	 */
 	@Override
 	float getBelowThresholdAllowed() {
-		return 0.3f;
+		return 0.15f;
 	}
 
 	@Override
 	float getOverThresholdAllowed() {
-		return 0.1f;
+		return 0.05f;
 	}
 
 }