Day 06 - Prepare to Step Into GUI

Today, we start to draw rectangles in C++.

Assembly Codes

• loader.asm

• func.asm

C++ Code

• kmain.cpp

Linking Template

• linker.ld

Makefile

• makefile

C++ Implementation

So far, the VGA is configured to be in Text mode. Draw a rectangle is equivalent to print colored empty charactor at specific locations on the screen. The core code reads

int main(){
    /* some other codes */

    boxfill8(p, SCREENX, RED, 0, 5, 10, 12); // from (0, 5) to (10, 12)
    boxfill8(p, SCREENX, GREEN, 50, 12, 70, 23);
    boxfill8(p, SCREENX, DARKBLUE, 79, 23, 80, 24);

    return 0;
}

void boxfill8(char *vram, int xsize, unsigned char c, int x0, int y0, int x1, int y1){
    /*
    * This function will draw a box (rectangle) on the screen which has width xsize
    * c is for color
    * (x0, y0) and (x1, y1) are two diagonals of the box. These are absolute coordinates
    */
    int x, y;
    if(y0 > y1){
        y = y0; y0 = y1; y1 = y;
    }
    if(x0 > x1){
        x = x0; x0 = x1; x1 = x;
    }

    for (y = y0; y < y1; y++){
        for(x = x0; x < x1; x++){
            vram[y * xsize*2 + x*2+1] = c<<4;
        }
    }
}

Result