Add framebuffer backbuffer implementation

Makefile

@@ -38,12 +38,13 @@ TARGET_ISO = $(OUT)/edgeos.iso
 ISO_DIR = $(OUT)/isodir
 
 OBJECTS = $(ASM_OBJ)/entry.o $(ASM_OBJ)/load_gdt.o\
-          $(ASM_OBJ)/load_idt.o $(ASM_OBJ)/exception.o $(ASM_OBJ)/irq.o\
-          $(OBJ)/io_ports.o $(OBJ)/vga.o\
-          $(OBJ)/string.o $(OBJ)/console.o\
-          $(OBJ)/gdt.o $(OBJ)/idt.o $(OBJ)/isr.o $(OBJ)/8259_pic.o\
-          $(OBJ)/keyboard.o\
-          $(OBJ)/kernel.o\
+	  $(ASM_OBJ)/load_idt.o $(ASM_OBJ)/exception.o $(ASM_OBJ)/irq.o\
+	  $(OBJ)/io_ports.o $(OBJ)/vga.o\
+	  $(OBJ)/fb.o\
+	  $(OBJ)/string.o $(OBJ)/console.o\
+	  $(OBJ)/gdt.o $(OBJ)/idt.o $(OBJ)/isr.o $(OBJ)/8259_pic.o\
+	  $(OBJ)/keyboard.o\
+	  $(OBJ)/kernel.o\
 		  $(OBJ)/stdio.o\
 		  $(OBJ)/fs.o
 
@@ -94,6 +95,11 @@ $(OBJ)/vga.o : $(SRC)/vga.c
 	$(CC) $(CFLAGS) -c $(SRC)/vga.c -o $(OBJ)/vga.o
 	@printf "\n"
 
+$(OBJ)/fb.o : $(SRC)/fb.c
+	@printf "[ $(SRC)/fb.c ]\n"
+	$(CC) $(CFLAGS) -c $(SRC)/fb.c -o $(OBJ)/fb.o
+	@printf "\n"
+
 $(OBJ)/string.o : $(SRC)/string.c
 	@printf "[ $(SRC)/string.c ]\n"
 	$(CC) $(CFLAGS) -c $(SRC)/string.c -o $(OBJ)/string.o

include/fb.h

@@ -0,0 +1,26 @@
+#ifndef FB_H
+#define FB_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+typedef struct {
+    uint8_t *addr;
+    uint32_t width;
+    uint32_t height;
+    uint32_t pitch;
+    uint32_t bpp;
+    uint32_t r_mask, g_mask, b_mask;
+    uint32_t r_pos, g_pos, b_pos;
+} fb_t;
+
+extern fb_t fb;
+
+bool fb_init_from_multiboot2(void *mb_info);
+void fb_debug_dump(void);
+void fb_putpixel(int x, int y, uint32_t argb);
+void fb_clear(uint32_t argb);
+bool fb_enable_backbuffer(void);
+void fb_present(void);
+
+#endif /* FB_H */

src/fb.c

@@ -0,0 +1,125 @@
+#include "fb.h"
+#include "string.h"
+#include <stddef.h>
+#include "console.h"
+
+fb_t fb = {0};
+
+static uint8_t *fb_backbuffer = NULL;
+#define FB_BACKBUFFER_MAX (1024*768*4)
+static uint8_t fb_backbuffer_storage[FB_BACKBUFFER_MAX]; /* up to 1024x768x32 */
+
+#define ALIGN_UP(v, a) (((v) + (a) - 1) & ~((a) - 1))
+
+struct multiboot_tag {
+    uint32_t type;
+    uint32_t size;
+};
+
+struct multiboot_tag_framebuffer {
+    struct multiboot_tag tag;
+    uint64_t framebuffer_addr;
+    uint32_t framebuffer_pitch;
+    uint32_t framebuffer_width;
+    uint32_t framebuffer_height;
+    uint8_t framebuffer_bpp;
+    uint8_t framebuffer_type;
+    uint16_t reserved;
+    union {
+        struct {
+            uint32_t framebuffer_palette_addr;
+            uint16_t framebuffer_palette_num_colors;
+        };
+        struct {
+            uint8_t framebuffer_red_field_position;
+            uint8_t framebuffer_red_mask_size;
+            uint8_t framebuffer_green_field_position;
+            uint8_t framebuffer_green_mask_size;
+            uint8_t framebuffer_blue_field_position;
+            uint8_t framebuffer_blue_mask_size;
+        };
+    };
+};
+
+static uint32_t fb_argb_to_pixel(uint32_t argb) {
+    uint32_t r = (argb >> 16) & 0xFF;
+    uint32_t g = (argb >> 8) & 0xFF;
+    uint32_t b = argb & 0xFF;
+    uint32_t pixel = (r << fb.r_pos) & fb.r_mask;
+    pixel |= (g << fb.g_pos) & fb.g_mask;
+    pixel |= (b << fb.b_pos) & fb.b_mask;
+    return pixel;
+}
+
+bool fb_init_from_multiboot2(void *mb_info) {
+    if (!mb_info)
+        return false;
+    uint8_t *ptr = (uint8_t *)mb_info;
+    struct multiboot_tag *tag = (struct multiboot_tag *)(ptr + 8);
+    while (tag->type != 0) {
+        if (tag->type == 8) {
+            struct multiboot_tag_framebuffer *fbtag = (struct multiboot_tag_framebuffer *)tag;
+            if (fbtag->framebuffer_type != 1)
+                return false;
+            fb.addr = (uint8_t *)(uintptr_t)fbtag->framebuffer_addr;
+            fb.pitch = fbtag->framebuffer_pitch;
+            fb.width = fbtag->framebuffer_width;
+            fb.height = fbtag->framebuffer_height;
+            fb.bpp = fbtag->framebuffer_bpp;
+            fb.r_pos = fbtag->framebuffer_red_field_position;
+            fb.g_pos = fbtag->framebuffer_green_field_position;
+            fb.b_pos = fbtag->framebuffer_blue_field_position;
+            fb.r_mask = ((1u << fbtag->framebuffer_red_mask_size) - 1u) << fb.r_pos;
+            fb.g_mask = ((1u << fbtag->framebuffer_green_mask_size) - 1u) << fb.g_pos;
+            fb.b_mask = ((1u << fbtag->framebuffer_blue_mask_size) - 1u) << fb.b_pos;
+            return true;
+        }
+        tag = (struct multiboot_tag *)((uint8_t *)tag + ALIGN_UP(tag->size, 8));
+    }
+    return false;
+}
+
+void fb_debug_dump(void) {
+    console_printf("FB addr=%p size=%ux%u pitch=%u bpp=%u\n",
+                   fb.addr, fb.width, fb.height, fb.pitch, fb.bpp);
+    console_printf("R: mask=%08x pos=%u\n", fb.r_mask, fb.r_pos);
+    console_printf("G: mask=%08x pos=%u\n", fb.g_mask, fb.g_pos);
+    console_printf("B: mask=%08x pos=%u\n", fb.b_mask, fb.b_pos);
+}
+
+void fb_putpixel(int x, int y, uint32_t argb) {
+    if (!fb.addr)
+        return;
+    if ((unsigned)x >= fb.width || (unsigned)y >= fb.height)
+        return;
+    uint8_t *base = fb_backbuffer ? fb_backbuffer : fb.addr;
+    uint32_t pixel = fb_argb_to_pixel(argb);
+    *(uint32_t *)(base + y * fb.pitch + x * (fb.bpp / 8)) = pixel;
+}
+
+void fb_clear(uint32_t argb) {
+    if (!fb.addr)
+        return;
+    uint8_t *base = fb_backbuffer ? fb_backbuffer : fb.addr;
+    uint32_t pixel = fb_argb_to_pixel(argb);
+    for (uint32_t y = 0; y < fb.height; y++) {
+        uint32_t *row = (uint32_t *)(base + y * fb.pitch);
+        for (uint32_t x = 0; x < fb.width; x++) {
+            row[x] = pixel;
+        }
+    }
+}
+
+bool fb_enable_backbuffer(void) {
+    size_t size = fb.pitch * fb.height;
+    if (size > FB_BACKBUFFER_MAX)
+        return false;
+    fb_backbuffer = fb_backbuffer_storage;
+    return true;
+}
+
+void fb_present(void) {
+    if (!fb.addr || !fb_backbuffer)
+        return;
+    memcpy(fb.addr, fb_backbuffer, fb.pitch * fb.height);
+}