changes from smg

src/pc80/vga_load_pcx.c

@@ -4,7 +4,7 @@
  * $Source$
  *
  * load a splash image from a pcx file
- * the pcs file is stored in flash at a know address.
+ * the pcs file is stored in flash at a known address.
  * VGA must be in gmode prior to entering this routine.
  * There are some assumptions made about the pcx image
  * and the color table. See the code.
@@ -12,6 +12,10 @@
  * by 
  * Steve M. Gehlbach <steve@kesa.com>
  *
+ * References: 
+ * PCX file spec:
+ *       http://www.whisqu.se/per/docs/graphics57.htm
+ *
  * pcx row decode function modified from the netpbm project
  * http://download.sourceforge.net/netpbm/
  *
@@ -28,9 +32,11 @@ u8 *vga = (u8 *) VGA_GRAFIX_BASE;
 static void GetPCXRow(unsigned char * pcx_file, unsigned char * const pcxrow, int const bytesperline, int * file_index);
 void writeVga(u8 *pcxrow);
 
+// globals
 static int rowsRead = 0;
 static int xsize = 0;
 static int ysize = 0;
+static u8 p_offset;
 
 struct pcx_header {
 	u8 manufacturer;
@@ -58,6 +64,31 @@ int vga_load_pcx (char * pcx_file, int size) {
 	u8 vgarow[650];
 	struct pcx_header *pcx;
 
+/////////////////////////////////////////////////////////////////////
+//  
+//  Image must be 1 plane, 8 bits per pixel, run length encoding, 
+//  256 colors with only 16 colors of the 256 used.  The file is 
+//  assumed to be a version 5 type file with the 256 
+//  color palette at the file end.  Only 4 bit planes
+//  are used, however, so the image must be generated with
+//  16 colors, so that the palette uses only 16
+//  entries.  The image can use either the bottom or
+//  top of the palette (the code checks the
+//  bottom then the top of 256 entry palette).  
+//  Gimp puts the 16 entry palette at the beginning of the 256 color
+//  palette, and PhotoShop puts the 16 colors at the end of the palette.
+//  Both are supported.  To generate a compatible pcx file in gimp,
+//  right click on the image and select image->mode->indexed, 
+//  change #colors to 16, and make sure "Generate Optimal Palette"
+//  and appropriate dithering is selected (Floyd Steinberg Normal
+//  is the default and seems to work).  Click Okay, then right
+//  click and select File->Save As and select PCX as the File
+//  Type and save the file with a pcx extension.
+//  This routine supports variable width and height but the default
+//  for linuxbios is 640 x 400 pixels.
+//
+/////////////////////////////////////////////////////////////////////
+
 	pcx = (struct pcx_header *) pcx_file;
 	if ( ! (pcx->manufacturer == 0x0a && pcx->version == 0x05 && pcx->encoding == 0x01) ) {
 		printk_info("vga_load_pcx: not a compatible .pcx file.\n");
@@ -83,22 +114,35 @@ int vga_load_pcx (char * pcx_file, int size) {
 			total_bytes_per_line*ysize		
 			);
 
-	// read the color table at the end of the file
-	// skip first 240 colors
-	// we only use last 16 colors
+	// Read the color table at the end of the file.
+	// Check the beginning of the palette to see if it
+	// is non-zero.  Default to the end of the palette
+	// if beginning is zero.  We only use 16 colors.
 
 	file_index = size-769;
+	// check palette signature
 	if (pcx_file[file_index++] != PCX_256_COLORS) {
+		// palette no good, bail out
 		printk_info("vga_load_pcx: invalid color table signature at file_index %d: 0x%x\n",
 				file_index-1,pcx_file[file_index-1]);
 				return -1;
 		}
-	file_index += 240*3; 
+	
+	// add up 2 3-tuples at beginning of palette and see if the result == 0; if so,
+	// then use top 16 entries.  If not, then use 16 entries at beginning of palette.
+	p_offset = 0;
+	for (i = 0; i<6; i++) p_offset += pcx_file[file_index + i];
+	if (p_offset == 0) p_offset = 240;
+	else p_offset = 0;
+
+	file_index += p_offset*3; 
 	i = 0;
 	outb_p(240, PEL_IW);
 	do {
-		// put the 16 3-tuple color table at the top of the PEL
-		// scale 0-255 -> 0-63
+		// put the 16 3-tuple color table at the upper end of the PEL
+		// this avoids conflicting with standard palette at lower end
+		// since the upper end is not used in this legacy mode
+		// scale 0-255 -> 0-63 (6 bit DAC)
 		outb_p(pcx_file[file_index++]>>2, PEL_D);
 		outb_p(pcx_file[file_index++]>>2, PEL_D);
 		outb_p(pcx_file[file_index++]>>2, PEL_D);
@@ -110,6 +154,7 @@ int vga_load_pcx (char * pcx_file, int size) {
 		printk_debug("vga_load_pcx: %d colors read into colortable.\n",i);
 
 	// set the color select to set b7-4 to 1111 to use high end of PEL
+	// this avoids conflicting with standard palette at lower end
 	write_att(read_att_b(ATC_MODE)|0x80,ATC_MODE);
 	write_att(0x0f,ATC_COLOR_PAGE);
 	
@@ -211,8 +256,9 @@ void writeVga(u8 *pcxrow) {
 			}
 			if (i >= xsize) return;
 		}
-	// pixel value is at high end so subtract 240
-		s_pixel = pcxrow[i] - 240;
+	// if we are using upper end of palette, then
+	// subtract 240 to scale value to 0-15
+		s_pixel = pcxrow[i] - p_offset;
 		mask = 0x80 >> (i % 8);
 		for (j=0;j<4;j++)
 			if (s_pixel & (1<<j) )