cores/video: Change the color lookup algo for direct mode

This allows to have 4 customizable color per glyphs (2 pairs).

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

cores/video/doc/text-mode.md

@@ -198,14 +198,15 @@ in the attributes.
 
 Assuming `px` is the value from the glyph, color lookup is done like this :
 
- * `0000`: Perform lookup in palette `0` for color index `bg`
- * `0001`: Perform lookup in palette `0` for color index `8+fg`
+ * `00x0`: Perform lookup in palette `0` for color index `{ x, bg }`
+ * `00y1`: Perform lookup in palette `0` for color index `{ y, fg }`
  * Other value: Perform lookup in palette `1` for color index `px`
 
-This allows to have color `0` and `1` of the glyphs be mapped to 8 possible
-background and 8 possible foreground colors. Those can be freely chosen and
-defined in palette `0`, the first 8 entries being background colors and the
-last 8 entries being foreground colors.
+This allows the first 4 colors to be customized directly per character and
+remapped. For instance to change text color without need for different glyphs.
+The default for a monochrome font would be to have `x = 0` and `y = 1` so
+that in palette `0`, the first 8 entries are background colors and the last
+8 entries are foreground ones.
 
 If the glyph uses other colors, then those are looked up directly in palette
 `1`. This way the glyph can also use static colors that don't depend on the

cores/video/rtl/vid_text.v

@@ -414,8 +414,8 @@ module vid_color_map (
 	always @(*)
 	begin
 		if (attrs[1]) begin
-			if (glyph[3:1] == 3'b000)
-				color <= { 4'b0000, glyph[0], glyph[0] ? attrs[7:5] : attrs[4:2] };
+			if (glyph[3:2] == 2'b00)
+				color <= { 4'b0000, glyph[1], glyph[0] ? attrs[7:5] : attrs[4:2] };
 			else
 				color <= { 4'b0001, glyph };
 		end else begin