wrote FbConverter class earlier but then realized it is not necessary…

…, so put it in experiments

experiments/fbconvert.cpp

@@ -0,0 +1,72 @@
+class FbConverter {
+    int bpp, depth,
+        red_max, green_max, blue_max,
+        red_shift, green_shift, blue_shift;
+
+public:
+    FbConverter(int bbpp, int ddepth,
+        int rred_max, int ggreen_max, int bblue_max,
+        int rred_shift, int ggreen_shift, int bblue_shift) :
+        bpp(bbpp), depth(ddepth),
+        red_max(rred_max), green_max(ggreen_max), blue_max(bblue_max),
+        red_shift(rred_shift), green_shift(ggreen_max), blue_shift(bblue_shift) {}
+
+    FbConverter() {}
+
+    unsigned char *
+    to_rgba(const unsigned char *input, int width, int height) {
+        int depth_shift = 0;
+        if (bpp != depth) depth_shift = bpp-depth;
+
+        int new_length = 4 * width * height;
+        unsigned char *output = (unsigned char *)
+            malloc(sizeof(unsigned char) * new_length);
+        if (!output) {
+            ThrowException(Exception::Error(
+                String::New("malloc failed in node-png (FbConverter::to_rgba).")
+            ));
+        }
+
+        // couldn't yet figure out how to avoid all this copy/paste based on
+        // bpp size.
+        if (bpp == 8) {
+            unsigned char val;
+            for (int i = 0, j = 0; i < width*height*bpp/8; i+=bpp/8, j+=4) {
+                val = (char)(input[i] >> depth_shift);
+                output[j] = (val >> red_shift) & red_max;
+                output[j+1] = (val >> green_shift) & green_max;
+                output[j+2] = (val >> blue_shift) & blue_max;
+                output[j+3] = 0xFF;
+            }
+        }
+        else if (bpp == 16) {
+            unsigned int val;
+            for (int i = 0, j = 0; i < width*height*bpp/8; i+=bpp/8, j+=4) {
+                val = (unsigned int)(input[i] >> depth_shift);
+                output[j] = (val >> red_shift) & red_max;
+                output[j+1] = (val >> green_shift) & green_max;
+                output[j+2] = (val >> blue_shift) & blue_max;
+                output[j+3] = 0xFF;
+            }
+        }
+        else if (bpp == 32) {
+            unsigned long val;
+            for (int i = 0, j = 0; i < width*height*bpp/8; i+=bpp/8, j+=4) {
+                val = (unsigned long)(input[i] >> depth_shift);
+                output[j] = (val >> red_shift) & red_max;
+                output[j+1] = (val >> green_shift) & green_max;
+                output[j+2] = (val >> blue_shift) & blue_max;
+                output[j+3] = depth == 32 ? val&0xFF : 0xFF;
+            }
+
+        }
+        else {
+            char message[100];
+            snprintf(message, 100, "Unknown bpp size %d", bpp);
+            ThrowException(Exception::Error(String::New(message)));
+        }
+
+        return output;
+    }
+};
+