Clarify 2nd order filter code.

console/js/dt_ui.js

@@ -29,6 +29,7 @@ dt_ui_color_text_title = "blue";
 dt_ui_color_background = "lightgrey";
 dt_ui_color_background_value = "white";
 dt_ui_color_background_title = "silver";
+dt_ui_color_border = "black";
 dt_ui_color_indicator_off = "grey";
 dt_ui_color_indicator_green = "#00ff00";
 dt_ui_color_indicator_red = "#ff0000";
@@ -274,7 +275,7 @@ function dt_ui_canvas(elementid)
 
 	this.element.style.borderStyle = "solid";
 	this.element.style.borderWidth = "1px";
-	this.element.style.borderColor = "black";
+	this.element.style.borderColor = dt_ui_color_border;
 
 	dt_ui_element.call(this, elementid);
 }
@@ -286,7 +287,7 @@ function dt_ui_title(elementid)
 	dt_ui_element.call(this, elementid);
 	this.title_set("untitled");
 	this.element.style.whiteSpace = "nowrap";
-	this.element.style.borderColor = "black";
+	this.element.style.borderColor = dt_ui_color_border;
 	this.element.style.borderStyle = "solid";
 	this.element.style.borderTopWidth = "0px";
 	this.element.style.borderBottomWidth = "1px";
@@ -321,7 +322,9 @@ function dt_ui_window(elementid)
 	this.content.padding_height = dt_ui_padding_height_window;
 	this.content.padding_width = dt_ui_padding_width_window;
 
-	this.element.style.border = "thin solid black";
+	this.element.style.border = "thin";
+	this.element.style.borderColor = dt_ui_color_border;
+	this.element.style.borderStyle = "solid";
 	this.element.style.background = dt_ui_color_background;
 	this.element.style.position = "relative";
 }
@@ -408,7 +411,7 @@ function dt_ui_value(elementid)
 	this.align = "center";
 	this.element.style.borderStyle = "solid";
 	this.element.style.borderWidth = "1px";
-	this.element.style.borderColor = "black";
+	this.element.style.borderColor = dt_ui_color_border;
 	this.element.style.background = dt_ui_color_background_value;
 	this.element.style.alignContent = "center";
 	this.element.style.textAlign = this.align;

controller/block/block_filter_iir.c

 /*
-	Copyright Jeroen Vreeken (pe1rxq@amsat.org), 2007
+	Copyright Jeroen Vreeken (jeroen@vreeken.net), 2007, 2015
 	Copyright Stichting C.A. Muller Radioastronomiestation, 2007
 
 	This program is free software: you can redistribute it and/or modify
@@ -49,6 +49,11 @@ struct controller_block_private {
 	struct block_filter_iir_param param;
 };
 
+#define INDEX_ZERO 1
+#define INDEX_POLE 0
+#define INDEX_X 2
+#define INDEX_Y 3
+
 static void filter_iir_calculate(struct controller_block *iir)
 {
 	struct controller_block_private *priv = iir->private;
@@ -59,7 +64,7 @@ static void filter_iir_calculate(struct controller_block *iir)
 	float out;
 
 	ind = priv->ind;
-	transfer[ind][2] = input0;
+	transfer[ind][INDEX_X] = input0;
 	len = priv->len;
 	ind++;
 	ind = ind % len;
@@ -70,10 +75,10 @@ static void filter_iir_calculate(struct controller_block *iir)
 	for (i = 0; i < len; i++) {
 		int j = (i + ind) % len;
 		
-		out += transfer[i][1] * transfer[j][2];
-		out += transfer[i][0] * transfer[j][3];
+		out += transfer[i][INDEX_ZERO] * transfer[j][INDEX_X];
+		out += transfer[i][INDEX_POLE] * transfer[j][INDEX_Y];
 	}
-	transfer[ind][3] = out;
+	transfer[ind][INDEX_Y] = out;
 
 	priv->out = out;
 }
@@ -108,18 +113,20 @@ static int param_set(struct controller_block *iir, char *param, int argc,
 		iir->private->len = 0;
 		return -1;
 	}
-	iir->private->transfer[0][0] = 0;
-	iir->private->transfer[iir->private->param.len ][1] =
+	/* All zeros are prescaled with inverse gain */
+	iir->private->transfer[0][INDEX_POLE] = 0;
+	/* x0 input coefficient is always 1.0 */
+	iir->private->transfer[iir->private->param.len ][INDEX_ZERO] =
 	    1.0 / iir->private->param.gain;
 	for (i = 0; i < iir->private->param.len; i++) {
-		iir->private->transfer[i + 1][0] =
+		iir->private->transfer[i + 1][INDEX_POLE] =
 		    iir->private->param.poles[i];
-		iir->private->transfer[i][1] =
+		iir->private->transfer[i][INDEX_ZERO] =
 		    iir->private->param.zeros[i] / iir->private->param.gain;
 	}
 	for (i = 0; i < iir->private->len; i++) {
-		iir->private->transfer[i][2] = 0;
-		iir->private->transfer[i][3] = 0;
+		iir->private->transfer[i][INDEX_X] = 0;
+		iir->private->transfer[i][INDEX_Y] = 0;
 	}
 	iir->private->ind = 0;
 	iir->private->out = 0;