汇编语言用“*”画一个圆，要求“*”为红色

汇编语言并不直接支持颜色的设置，但可以通过调用操作系统提供的API来实现。以下是在Windows系统下用MASM汇编语言画一个红色“*”的圆的示例代码：

.386
.model flat, stdcall
option casemap:none

include windows.inc
include kernel32.inc
include user32.inc

includelib kernel32.lib
includelib user32.lib

.data
    ClassName db "myWindowClass", 0
    WindowName db "My Window", 0
    Red db 255, 0, 0

.const
    RADIUS equ 50
    PI equ 3.14159265358979323846

.data?
    hInstance HINSTANCE ?
    hWnd HWND ?
    msg MSG ?
    wc WNDCLASSEX ?

.code
start:
    invoke GetModuleHandle, NULL
    mov hInstance, eax

    xor eax, eax
    mov wc.cbSize, sizeof WNDCLASSEX
    mov wc.style, CS_HREDRAW or CS_VREDRAW
    mov wc.lpfnWndProc, OFFSET WndProc
    mov wc.cbClsExtra, 0
    mov wc.cbWndExtra, 0
    push hInstance
    pop wc.hInstance
    mov wc.hbrBackground, COLOR_WINDOW + 1
    mov wc.lpszMenuName, NULL
    mov wc.lpszClassName, OFFSET ClassName
    invoke LoadIcon, NULL, IDI_APPLICATION
    mov wc.hIcon, eax
    mov wc.hIconSm, eax
    invoke LoadCursor, NULL, IDC_ARROW
    mov wc.hCursor, eax
    invoke RegisterClassEx, addr wc

    invoke CreateWindowEx, NULL, OFFSET ClassName, OFFSET WindowName, \
           WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, \
           640, 480, NULL, NULL, hInstance, NULL
    mov hWnd, eax
    invoke ShowWindow, hWnd, SW_SHOWNORMAL
    invoke UpdateWindow, hWnd

    .while TRUE
        invoke GetMessage, ADDR msg, NULL, 0, 0
        .break .if(!eax)
        invoke TranslateMessage, ADDR msg
        invoke DispatchMessage, ADDR msg
    .endw

    mov eax, msg.wParam
    ret

WndProc PROC hWnd:HWND, uMsg:UINT, wParam:WPARAM, lParam:LPARAM
    .if uMsg == WM_DESTROY
        invoke PostQuitMessage, NULL
    .elseif uMsg == WM_PAINT
        invoke BeginPaint, hWnd, ADDR ps
        invoke GetClientRect, hWnd, ADDR rect
        mov eax, rect.right
        sub eax, rect.left
        mov ecx, 2
        div ecx
        mov ebx, eax
        mov eax, rect.bottom
        sub eax, rect.top
        div ecx
        mov edx, eax
        invoke CreateSolidBrush, RGB Red
        mov hBrush, eax
        invoke SelectObject, ps.hdc, hBrush
        mov eax, ebx
        sub eax, RADIUS
        mov ecx, edx
        sub ecx, RADIUS
        mov esi, 0
        mov edi, 0
        .while eax <= ebx
            .while ecx <= edx
                mov ebx, eax
                sub ebx, esi
                imul ebx, ebx
                mov ecx, edx
                sub ecx, edi
                imul ecx, ecx
                add ebx, ecx
                mov ecx, RADIUS
                imul ecx, ecx
                .if ebx <= ecx
                    invoke SetPixel, ps.hdc, eax, ecx, RGB Red
                .endif
                add ecx, 1
            .endw
            add eax, 1
        .endw
        invoke EndPaint, hWnd, ADDR ps
    .else
        invoke DefWindowProc, hWnd, uMsg, wParam, lParam
        ret
    .endif
    xor eax, eax
    ret
WndProc ENDP

end start

在上面的代码中，我们首先定义了一个半径为50的圆，然后在WM_PAINT消息中使用CreateSolidBrush函数创建一个红色的画刷，设置画刷颜色为RGB(Red)。接着，我们使用SetPixel函数在圆的周围绘制红色的像素点，从而形成一个红色的圆。

需要注意的是，该示例只是为了演示如何使用汇编语言画一个红色的圆，实际应用中可能需要更加复杂的绘图算法和图形界面库，例如OpenGL。