gdi32: Calculate the min/max color component intensities for 17 glyph levels.

dlls/gdi32/dibdrv/dc.c

@@ -528,6 +528,7 @@ static COLORREF dibdrv_SetTextColor( PHYSDEV dev, COLORREF color )
     dibdrv_physdev *pdev = get_dibdrv_pdev(dev);
 
     pdev->text_color = get_pixel_color( pdev, color, TRUE );
+    update_aa_ranges( pdev );
 
     return next->funcs->pSetTextColor( next, color );
 }

dlls/gdi32/dibdrv/dibdrv.h

@@ -67,6 +67,13 @@ typedef struct
     void *xor;
 } rop_mask_bits;
 
+struct intensity_range
+{
+    BYTE r_min, r_max;
+    BYTE g_min, g_max;
+    BYTE b_min, b_max;
+};
+
 typedef struct dibdrv_physdev
 {
     struct gdi_physdev dev;
@@ -100,6 +107,7 @@ typedef struct dibdrv_physdev
 
     /* text */
     DWORD text_color;
+    struct intensity_range glyph_intensities[17];
 } dibdrv_physdev;
 
 #define DEFER_FORMAT     1
@@ -218,6 +226,7 @@ extern HRGN add_extra_clipping_region( dibdrv_physdev *pdev, HRGN rgn ) DECLSPEC
 extern void restore_clipping_region( dibdrv_physdev *pdev, HRGN rgn ) DECLSPEC_HIDDEN;
 extern int clip_line(const POINT *start, const POINT *end, const RECT *clip,
                      const bres_params *params, POINT *pt1, POINT *pt2) DECLSPEC_HIDDEN;
+extern void update_aa_ranges( dibdrv_physdev *pdev ) DECLSPEC_HIDDEN;
 
 static inline BOOL defer_pen(dibdrv_physdev *pdev)
 {

dlls/gdi32/dibdrv/graphics.c

@@ -56,6 +56,53 @@ static RECT get_device_rect( HDC hdc, int left, int top, int right, int bottom,
     return rect;
 }
 
+/* Intensities of the 17 glyph levels when drawn with text component of 0xff on a
+   black bkgnd.  [A log-log plot of these data gives: y = 77.05 * x^0.4315]. */
+static const BYTE ramp[17] =
+{
+    0,    0x4d, 0x68, 0x7c,
+    0x8c, 0x9a, 0xa7, 0xb2,
+    0xbd, 0xc7, 0xd0, 0xd9,
+    0xe1, 0xe9, 0xf0, 0xf8,
+    0xff
+};
+
+/* For a give text-color component and a glyph level, calculate the
+   range of dst intensities, the min/max corresponding to 0/0xff bkgnd
+   components respectively.
+
+   The minimum is a linear interpolation between 0 and the value in
+   the ramp table.
+
+   The maximum is a linear interpolation between the value from the
+   ramp table read in reverse and 0xff.
+
+   To find the resulting pixel intensity, we note that if the text and
+   bkgnd intensities are the same then the result must be that
+   intensity.  Otherwise we linearly interpolate between either the
+   min or the max value and this intermediate value depending on which
+   side of the inequality we lie.
+*/
+
+static inline void get_range( BYTE aa, DWORD text_comp, BYTE *min_comp, BYTE *max_comp )
+{
+    *min_comp = (ramp[aa] * text_comp) / 0xff;
+    *max_comp = ramp[16 - aa] + ((0xff - ramp[16 - aa]) * text_comp) / 0xff;
+}
+
+void update_aa_ranges( dibdrv_physdev *pdev )
+{
+    int i;
+    COLORREF text = pdev->dib.funcs->pixel_to_colorref( &pdev->dib, pdev->text_color );
+
+    for (i = 0; i < 17; i++)
+    {
+        get_range( i, GetRValue(text), &pdev->glyph_intensities[i].r_min, &pdev->glyph_intensities[i].r_max );
+        get_range( i, GetGValue(text), &pdev->glyph_intensities[i].g_min, &pdev->glyph_intensities[i].g_max );
+        get_range( i, GetBValue(text), &pdev->glyph_intensities[i].b_min, &pdev->glyph_intensities[i].b_max );
+    }
+}
+
 /**********************************************************************
  *                 get_text_bkgnd_masks
  *