add apng preanims

1 files changed, 26 insertions, 0 deletions

diff --git a/webAO/utils/calculateApngLength.js b/webAO/utils/calculateApngLength.js
new file mode 100644
index 0000000..bc6b3fa
--- /dev/null
+++ b/webAO/utils/calculateApngLength.js
@@ -0,0 +1,26 @@
+	/**
+	 * Adds up the chunk delays to find out how long a APNG is
+	 * @param {data} apngFile the APNG data
+	 */
+const calculateApngLength = (apngFile) => {
+  const d = new Uint8Array(apngFile);
+			// https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk
+			let duration = 0;
+			for (var i = 0; i < d.length; i++) {
+				// Find fcTL header (66 63 54 4C)
+				if (d[i] === 0x66
+					&& d[i + 1] === 0x63
+					&& d[i + 2] === 0x54
+					&& d[i + 3] === 0x4C) {
+					console.log("found apng header");
+					// numerator and denominator
+					let delay = ((d[i + 21] / d[i + 23]) * 1000)
+
+					// minimum is 100ms
+					duration += delay < 100 ? 100 : delay;
+				}
+			}
+			console.debug(duration);
+			return duration * 10;
+};
+export default calculateApngLength;