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lib: Implement resolution-based text scaling

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Add support for dynamic text scaling based on the display resolution
to ensure bootsplash text remains legible on high-density panels.

Key changes:
- Implement get_resolution_scale() to determine a scaling factor (1x,
  2x, or 3x) based on the panel's major dimension (HD, QHD, or 4K).
- Update draw_char() to render glyphs as scaled blocks, repeating each
  font pixel across a square of the calculated scale factor.
- Apply the scaling factor to all text layout calculations, including
  kerning, character advance, and total string dimensions.
- Ensure anti-aliasing (alpha blending) is correctly applied to each
  individual pixel within the scaled blocks.

Change-Id: I8b22019ddaa46f1a24f38d565d946bb28a213791
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/91182
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
This commit is contained in:
Subrata Banik 2026-02-12 18:37:37 +05:30
commit b9458ff2bc
1 changed files with 53 additions and 24 deletions
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73
src/lib/render_text.c
View file

@ -3,10 +3,30 @@
#include <bootsplash.h>
#include <console/console.h>
#include <stdlib.h>
#include <string.h>
#include "fonts/fonts.h"
#include "render_bmp.h"
/* Major dimension for panel */
#define PANEL_4K 3840
#define PANEL_2K_QHD 2560
/* Determine scaling factor based on display resolution */
static uint32_t get_resolution_scale(struct logo_config *config)
{
uint32_t width = config->horizontal_resolution;
uint32_t height = config->vertical_resolution;
uint32_t major_dim = (width > height) ? width : height;
if (major_dim >= PANEL_4K)
return 3;
else if (major_dim >= PANEL_2K_QHD)
return 2;
else /* HD / FHD Panels */
return 1;
}
/* Maps an unsigned character to the 8-bit alpha map (smoothing data) */
static const uint8_t *get_glyph_data(unsigned char c)
{
@ -61,7 +81,7 @@ static inline void get_rotated_text_coords(struct logo_config *config,
* @color: Primary text color.
*/
static void draw_char(struct logo_config *config, unsigned char c, uint32_t x, uint32_t y,
struct blt_pixel color)
struct blt_pixel color, uint32_t scale)
{
size_t pixel_size = sizeof(struct blt_pixel);
uint8_t *fb = (uint8_t *)config->framebuffer_base;
@ -77,23 +97,31 @@ static void draw_char(struct logo_config *config, unsigned char c, uint32_t x, u
if (alpha == 0)
continue;
uint32_t fb_x, fb_y;
get_rotated_text_coords(config, x, y, row, col, &fb_x, &fb_y);
/* Fill a scale x scale block for each font pixel */
for (uint32_t sy = 0; sy < scale; sy++) {
for (uint32_t sx = 0; sx < scale; sx++) {
uint32_t fb_x, fb_y;
get_rotated_text_coords(config, x, y,
(row * scale) + sy,
(col * scale) + sx,
&fb_x, &fb_y);
if (fb_x < config->horizontal_resolution &&
fb_y < config->vertical_resolution) {
if (fb_x < config->horizontal_resolution &&
fb_y < config->vertical_resolution) {
struct blt_pixel *bg = (struct blt_pixel *)
(fb + (fb_y * config->bytes_per_scanline) + (fb_x * pixel_size));
struct blt_pixel *bg = (struct blt_pixel *)
(fb + (fb_y * config->bytes_per_scanline) + (fb_x * pixel_size));
if (alpha == 255) {
/* Fully opaque: just overwrite */
*bg = color;
} else {
/* Perform Alpha Blending */
bg->Red = (uint8_t)((color.Red * alpha + bg->Red * (255 - alpha)) / 255);
bg->Green = (uint8_t)((color.Green * alpha + bg->Green * (255 - alpha)) / 255);
bg->Blue = (uint8_t)((color.Blue * alpha + bg->Blue * (255 - alpha)) / 255);
if (alpha == 255) {
*bg = color;
} else {
bg->Red = (uint8_t)((color.Red * alpha + bg->Red *
(255 - alpha)) / 255);
bg->Green = (uint8_t)((color.Green * alpha + bg->Green *
(255 - alpha)) / 255);
bg->Blue = (uint8_t)((color.Blue * alpha + bg->Blue *
(255 - alpha)) / 255);
}
}
}
}
}
@ -157,11 +185,12 @@ void render_text_to_framebuffer(struct logo_config *config, const char *str,
if (len == 0)
return;
const uint32_t kerning = 1;
uint32_t scale = get_resolution_scale(config);
const uint32_t kerning = 1 * scale;
uint32_t total_width = 0;
for (size_t i = 0; i < len; i++)
total_width += get_glyph_width((unsigned char)str[i]) + kerning;
total_width += (get_glyph_width((unsigned char)str[i]) * scale) + kerning;
uint32_t text_w, text_h;
enum fw_splash_horizontal_alignment halign;
@ -173,11 +202,11 @@ void render_text_to_framebuffer(struct logo_config *config, const char *str,
if (config->panel_orientation == LB_FB_ORIENTATION_LEFT_UP ||
config->panel_orientation == LB_FB_ORIENTATION_RIGHT_UP) {
text_w = CONFIG_FONT_HEIGHT;
text_w = CONFIG_FONT_HEIGHT * scale;
text_h = total_width;
} else {
text_w = total_width;
text_h = CONFIG_FONT_HEIGHT;
text_h = CONFIG_FONT_HEIGHT * scale;
}
struct logo_coordinates coords = calculate_logo_coordinates(config->horizontal_resolution,
@ -207,9 +236,9 @@ void render_text_to_framebuffer(struct logo_config *config, const char *str,
/* Loop through characters and draw them */
for (size_t i = 0; i < len; i++) {
unsigned char c = (unsigned char)str[i];
draw_char(config, c, cur_x, cur_y, text_color);
draw_char(config, c, cur_x, cur_y, text_color, scale);
uint32_t advance = get_glyph_width(c) + kerning;
uint32_t advance = (get_glyph_width(c) * scale) + kerning;
if (config->panel_orientation == LB_FB_ORIENTATION_RIGHT_UP)
cur_y += advance;
else if (config->panel_orientation == LB_FB_ORIENTATION_LEFT_UP)