add wasm source c file

src/imghelper.c

@@ -0,0 +1,38 @@
+#include <stdint.h>
+#include <stdbool.h>
+
+// Usage - generate js and wasm files
+// emcc imghelper.c -o imghelper.js -O2 -s WASM=1 -s EXPORTED_FUNCTIONS="['_copy_alpha_to_rgb','_check_alpha','_copy_alpha_channel','_malloc','_free']" -s EXPORTED_RUNTIME_METHODS="['ccall', 'cwrap']" -s ALLOW_MEMORY_GROWTH=1 -s MODULARIZE=1 -s EXPORT_ES6=1
+
+bool check_alpha(uint8_t *data, int pixelCount)
+{
+    for (int i = 0; i < pixelCount; ++i)
+    {
+        if (data[i * 4 + 3] != 255)
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
+void copy_alpha_to_rgb(uint8_t *source, uint8_t *target, int pixelCount)
+{
+    for (int i = 0; i < pixelCount; ++i)
+    {
+        uint8_t alpha = source[i * 4 + 3];
+        target[i * 4 + 0] = alpha;
+        target[i * 4 + 1] = alpha;
+        target[i * 4 + 2] = alpha;
+        target[i * 4 + 3] = alpha;
+    }
+}
+
+void copy_alpha_channel(uint8_t *source, uint8_t *target, int pixelCount)
+{
+    for (int i = 0; i < pixelCount; ++i)
+    {
+        uint8_t alpha = source[i * 4];
+        target[i * 4 + 3] = alpha;
+    }
+}