draw a character

Rsconscript

@@ -124,9 +124,9 @@ EOF
     env["LDFLAGS"] += %w[-ffreestanding -nostdlib -T src/link.ld]
     env["LIBS"] += %w[gcc]
     env["OBJDUMP"] = "i686-elf-objdump"
-    env.FontGen("^/fontgen/fontgen.c", "font/Hack-Regular.ttf")
-    env["CPPPATH"] += ["#{env.build_root}/fontgen"]
-    env.Program("^/hos.elf", glob("src/**/*.{S,c}") + ["^/fontgen/fontgen.c"])
+    env.FontGen("^/kfont/kfont.c", "font/Hack-Regular.ttf")
+    env["CPPPATH"] += ["#{env.build_root}/kfont"]
+    env.Program("^/hos.elf", glob("src/**/*.{S,c}") + ["^/kfont/kfont.c"])
     env.depends("#{env.build_root}/hos.elf", "src/link.ld")
     env.Disassemble("^/hos.elf.txt", "^/hos.elf")
     env.EfiImage("build/hos-efi.img", %w[^/hos.elf])

src/fb.c

@@ -6,6 +6,16 @@ static uint32_t fb_width;
 static uint32_t fb_height;
 static uint32_t fb_pitch;
 
+static inline uint32_t build_pixel(uint8_t r, uint8_t g, uint8_t b)
+{
+    return (r << 16u) | (g << 8u) | b;
+}
+
+static inline void fb_set_pixel(int x, int y, uint8_t r, uint8_t g, uint8_t b)
+{
+    fb[fb_pitch * y / 4u + x] = build_pixel(r, g, b);
+}
+
 void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch)
 {
     fb = addr;
@@ -34,3 +44,54 @@ bool fb_ready(void)
 {
     return fb != NULL;
 }
+
+void fb_blend_alpha8(const uint8_t * bitmap, int width, int height, int pitch, int x, int y, uint8_t r, uint8_t g, uint8_t b)
+{
+    if (((x + width) <= 0) || (x >= (int)fb_width) || ((y + height) <= 0) || (y >= (int)fb_height))
+    {
+        return;
+    }
+    if (x < 0)
+    {
+        width += x;
+        bitmap += (-x);
+        x = 0;
+    }
+    if (y < 0)
+    {
+        height += y;
+        bitmap += ((-y) * pitch);
+        y = 0;
+    }
+    if ((x + width) > (int)fb_width)
+    {
+        width = (int)fb_width - x;
+    }
+    if ((y + height) > (int)fb_height)
+    {
+        height = (int)fb_height - y;
+    }
+    uint32_t * target = &fb[fb_pitch * y / 4u + x];
+    for (int row = 0; row < height; row++)
+    {
+        for (int col = 0; col < width; col++)
+        {
+            uint32_t alpha = bitmap[col];
+            uint32_t current_pixel = target[col];
+            uint8_t cr = (current_pixel >> 16u) & 0xFFu;
+            uint8_t cg = (current_pixel >> 8u) & 0xFFu;
+            uint8_t cb = current_pixel & 0xFFu;
+            uint8_t pr = alpha * r / 255u;
+            uint8_t pg = alpha * g / 255u;
+            uint8_t pb = alpha * b / 255u;
+            uint32_t current_alpha = 255u - alpha;
+            uint32_t pixel = build_pixel(
+                    pr + current_alpha * cr / 255u,
+                    pg + current_alpha * cg / 255u,
+                    pb + current_alpha * cb / 255u);
+            target[col] = pixel;
+        }
+        bitmap += pitch;
+        target += (fb_pitch / 4u);
+    }
+}

src/fb.h

@@ -6,5 +6,6 @@
 
 void fb_init(uint32_t * addr, uint32_t width, uint32_t height, uint32_t pitch);
 bool fb_ready(void);
+void fb_blend_alpha8(const uint8_t * bitmap, int width, int height, int pitch, int x, int y, uint8_t r, uint8_t g, uint8_t b);
 
 #endif

src/hos_main.c

@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include "fb.h"
 #include "mbinfo.h"
+#include "kfont.h"
 
 void hos_main(uint32_t mbinfo_addr)
 {
@@ -9,4 +10,6 @@ void hos_main(uint32_t mbinfo_addr)
     {
         return;
     }
+    const fontgen_char_info_t * char_info = kfont.char_infos['H'];
+    fb_blend_alpha8(char_info->bitmap, char_info->width, char_info->height, char_info->width, 10, 10, 0xFFu, 0x88u, 0u);
 }