render: improve implementation of dpoly()

* Honor dwindow settings immediately (avoids useless dline() calls)
* Bound to ymin/ymax instead of doing many useless cut computations
* Remove the need for floating-point operations and division

CMakeLists.txt

@@ -107,6 +107,7 @@ set(SOURCES_COMMON
   src/render/dhline.c
   src/render/dimage.c
   src/render/dline.c
+  src/render/dpoly.c
   src/render/dprint.c
   src/render/drect_border.c
   src/render/dtext.c

include/gint/display.h

@@ -244,6 +244,21 @@ void dcircle(int xm, int ym, int r, int fill_color, int border_color);
 void dellipse(int x1, int y1, int x2, int y2, int fill_color,
    int border_color);
 
+/* dpoly(): Render an arbitrary polygon
+
+   Renders the polygon defined by vertices (x[i], y[i]) for 0 < i < N. A fill
+   color and border color can be specified separately. For filling, N must be
+   at least 3. For border, N must be at least 2.
+
+   Note: this is a fairly slow function, not designed for rendering triangles
+   in 3D games. There are faster methods for that.
+
+   @x @y          Arrays of vertex coordinates
+   @N             Number of vertices (length of x and y)
+   @fill_color    Color of the polygon's interior, C_NONE to disable
+   @border_color  Color of the polygon's border, C_NONE to disable */
+void dpoly(int const *x, int const *y, int N, int fill_color, int border_color);
+
 //---
 //	Text rendering (topti)
 //---

src/render/dpoly.c

@@ -1,67 +1,67 @@
 #include <gint/defs/util.h>
 #include <gint/display.h>
+#include <stdlib.h>
 
-void dpoly(int *polyX, int *polyY, int polyCorners, int fill_color, int border_color){
-
-  if (polyCorners<=2) return;
-
-  if (fill_color == C_NONE && border_color == C_NONE)
-    return;
-
-  if (fill_color != C_NONE) {
-    
-    float *nodeX, pixelX, pixelY, swap ;
-    int i, j, nodes;
-    
-    nodeX = malloc( polyCorners * sizeof(float));
-
-    //  Loop through the rows of the image.
-    for (pixelY=0; pixelY<DHEIGHT; pixelY++) {
-      
-      //  Build a list of nodes.
-      nodes=0; j=polyCorners-1;
-      for (i=0; i<polyCorners; i++) {
-        if ((polyY[i]<(float) pixelY && polyY[j]>=(float) pixelY)
-        ||  (polyY[j]<(float) pixelY && polyY[i]>=(float) pixelY)) {
-          nodeX[nodes++]=(int) (polyX[i]+(pixelY-polyY[i])/(polyY[j]-polyY[i])*(polyX[j]-polyX[i]));
-        }
-        j=i;
-      }
-
-      //  Sort the nodes, via a simple “Bubble” sort.
-      i=0;
-      while (i<nodes-1) {
-        if (nodeX[i]>nodeX[i+1]) {
-          swap=nodeX[i]; nodeX[i]=nodeX[i+1]; nodeX[i+1]=swap; if (i) i--;
-        }
-        else {
-          i++;
-        }
-      }
-
-      //  Fill the pixels between node pairs.
-      for (i=0; i<nodes; i+=2) {
-        if (nodeX[i  ]>=DWIDTH) break;
-        if (nodeX[i+1]<= 0 ) break;
-        if (nodeX[i  ]< 0 ) nodeX[i  ]=0 ;
-        if (nodeX[i+1]> DWIDTH) nodeX[i+1]=DWIDTH;
-        //for (pixelX=nodeX[i]; pixelX<nodeX[i+1]; pixelX++) fillPixel(pixelX,pixelY);
-        dline(nodeX[i], pixelY, nodeX[i+1], pixelY, fill_color);
-      }
-    }       
-
-    free(nodeX);
-  }
-
-  if (border_color != C_NONE) {
-    for (int i = 0; i < polyCorners; i++) {
-      int px = polyX[i];
-      int py = polyY[i];
-      int px2 = polyX[(i + 1) % polyCorners];
-      int py2 = polyY[(i + 1) % polyCorners];
-      dline(px, py, px2, py2, border_color);
-    }
-  }
-
-  return;
+static int compare(void const *ptr1, void const *ptr2)
+{
+	return *(int const *)ptr1 - *(int const *)ptr2;
+}
+
+static void dpoly_fill(int const *x, int const *y, int N, int color)
+{
+	int *nodeX = malloc(N * sizeof *nodeX);
+
+	/* Find vertical bounds */
+	int ymin = y[0], ymax = y[0];
+	for(int i = 1; i < N; i++)
+	{
+		ymin = min(ymin, y[i]);
+		ymax = max(ymax, y[i]);
+	}
+	ymin = max(ymin, dwindow.top);
+	ymax = min(ymax, dwindow.bottom);
+
+	/* For each row, find vertical cuts from the segments and fill in-between
+	   the cuts. */
+	for(int pixelY = ymin; pixelY <= ymax; pixelY++) {
+
+		/* Build a list of nodes */
+		int nodes = 0;
+		int j = N - 1;
+		for(int i = 0; i < N; i++)
+		{
+			if((y[i] < pixelY) != (y[j] < pixelY))
+				nodeX[nodes++] = x[i]+(pixelY-y[i])*(x[j]-x[i])/(y[j]-y[i]);
+			j = i;
+		}
+
+		/* Sort the cuts' positions */
+		qsort(nodeX, nodes, sizeof nodeX[0], compare);
+
+		/* Fill the pixels between cut pairs */
+		for(int i = 0; i < nodes; i += 2)
+		{
+			if(nodeX[i] >= dwindow.right || nodeX[i+1] < dwindow.left) break;
+			nodeX[i] = max(nodeX[i], dwindow.left);
+			nodeX[i+1] = min(nodeX[i+1], dwindow.right);
+			dline(nodeX[i], pixelY, nodeX[i+1], pixelY, color);
+		}
+	}
+
+	free(nodeX);
+}
+
+static void dpoly_border(int const *x, int const *y, int N, int color)
+{
+	for(int i = 0; i < N - 1; i++)
+		dline(x[i], y[i], x[i+1], y[i+1], color);
+	dline(x[N-1], y[N-1], x[0], y[0], color);
+}
+
+void dpoly(int const *x, int const *y, int N, int fill_color, int border_color)
+{
+	if(N > 2 && fill_color != C_NONE)
+		dpoly_fill(x, y, N, fill_color);
+	if(N >= 2 && border_color != C_NONE)
+		dpoly_border(x, y, N, border_color);
 }