Fix font clipping bug

When fonts completely fill a slot, any pixel touching a perimeter
border gets stretched due to clamping. To avoid this, add a 2% margin
around each slot.

1 files changed, 14 insertions, 4 deletions

diff --git a/TaSTT.shader b/TaSTT.shader
index 4ea7e99..d4f4faf 100644
--- a/TaSTT.shader
+++ b/TaSTT.shader
@@ -786,10 +786,20 @@
         int CHAR_COLS = 44;

 

         // OK, I know what cell I'm in. Now I need to know how far across it I

-        // am. Produce a float in the range [0, CHAR_COLS).

+        // am. Produce a float in the range [0, 1).

         float CHAR_FRAC_COL = uv.x * CHAR_COLS - floor(uv.x * CHAR_COLS);

         float CHAR_FRAC_ROW = uv.y * CHAR_ROWS - floor(uv.y * CHAR_ROWS);

 

+        // Avoid rendering pixels right on the edge of the slot. If we were to

+        // do this, then that value would get stretched due to clamping

+        // (AddMarginToUV), resulting in long lines on the edge of the display.

+        if (CHAR_FRAC_ROW < 0.01 ||

+            CHAR_FRAC_COL < 0.01 ||

+            CHAR_FRAC_ROW > 0.99 ||

+            CHAR_FRAC_COL > 0.99) {

+          return float2(0, 0);

+        }

+

         // This is the number of rows and columns in the actual texture.

         float LETTER_COLS = 128.0;

         float LETTER_ROWS = 64.0;

@@ -797,8 +807,8 @@
         float LETTER_COL = fmod(nth_letter, floor(LETTER_COLS));

         float LETTER_ROW = floor(LETTER_ROWS) - floor(nth_letter / floor(LETTER_COLS));

 

-        float LETTER_UV_ROW = (LETTER_ROW + CHAR_FRAC_ROW - 0.99) / LETTER_ROWS;

-        float LETTER_UV_COL = (LETTER_COL + CHAR_FRAC_COL - 0.01) / LETTER_COLS;

+        float LETTER_UV_ROW = (LETTER_ROW + CHAR_FRAC_ROW - 1.0) / LETTER_ROWS;

+        float LETTER_UV_COL = (LETTER_COL + CHAR_FRAC_COL) / LETTER_COLS;

 

         float2 result;

         result.x = LETTER_UV_COL;

@@ -1229,7 +1239,7 @@
         }

 

         float uv_x_margin = 0.03;

-        float uv_y_margin = 0.06;

+        float uv_y_margin = 0.03;

         uv = AddMarginToUV(uv, uv_x_margin, uv_y_margin);

 

         int2 letter_bytes = (int2) floor(GetLetterParameter(uv));