// cl main.c

#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdint.h>

#define Assert(c) do { if (!(c)) __debugbreak(); } while (0)

#pragma comment (lib, "user32.lib")
#pragma comment (lib, "gdi32.lib")

typedef uint32_t u32;

int ClientWidth;
int ClientHeight;
void *Memory;

void DrawPixel(int X, int Y, u32 Color) {
    u32 *Pixel = (u32 *)Memory;
    Pixel += Y * ClientWidth + X;
    *Pixel = Color;
}

void ClearScreen(u32 Color) {
    u32 *Pixel = (u32 *)Memory;
    for(int Index = 0; Index < ClientWidth * ClientHeight; ++Index) {
        *Pixel++ = Color;
    }
}

LRESULT CALLBACK WindowProc(HWND Window, UINT Message, WPARAM WParam, LPARAM LParam) {
    switch(Message) {
        case WM_DESTROY: {
            PostQuitMessage(0);
        } break;
        case WM_KEYDOWN: {
            switch(WParam) {
                case 'O': { 
                    DestroyWindow(Window); 
                } break;
            }
        } break;
        default: {
            return DefWindowProcW(Window, Message, WParam, LParam);
        }
    }
    
    return 0;
}

int WINAPI WinMain(HINSTANCE Instance, HINSTANCE PrevInstance, LPSTR Cmd, int CmdShow) {
    
    // Create a window.
    
    WNDCLASSW WindowClass = {
        .lpszClassName = L"MyWindowClass",
        .lpfnWndProc = WindowProc,
        .hInstance = Instance,
        .hCursor = LoadCursor(NULL, IDC_CROSS),
    };
    ATOM Atom = RegisterClassW(&WindowClass);
    Assert(Atom && "Failed to register a window");
    
    HWND Window = CreateWindowW(WindowClass.lpszClassName, L"Drawing Pixels", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, Instance, NULL);
    Assert(Window && "Failed to create a window");
    
    ShowWindow(Window, CmdShow);
    
    // Allocate memory.
    
    RECT Rect;
    GetClientRect(Window, &Rect);
    ClientWidth = Rect.right - Rect.left;
    ClientHeight = Rect.bottom - Rect.top;
    
    Memory = VirtualAlloc(0, ClientWidth * ClientHeight * 4, MEM_RESERVE|MEM_COMMIT, PAGE_READWRITE);
    
    // Create BITMAPINFO struct for StretchDIBits().
    
    BITMAPINFO BitmapInfo;
    BitmapInfo.bmiHeader.biSize = sizeof(BitmapInfo.bmiHeader);
    BitmapInfo.bmiHeader.biWidth = ClientWidth;
    // Negative biHeight makes top left as the coordinate system origin. Otherwise it's bottom left.
    BitmapInfo.bmiHeader.biHeight = -ClientHeight;
    BitmapInfo.bmiHeader.biPlanes = 1;
    BitmapInfo.bmiHeader.biBitCount = 32;
    BitmapInfo.bmiHeader.biCompression = BI_RGB;
    
    HDC DeviceContext = GetDC(Window);
    
    for(;;) {
        MSG Message;
        if(PeekMessage(&Message, NULL, 0, 0, PM_REMOVE)) {
            if(Message.message == WM_QUIT) break;
            TranslateMessage(&Message);
            DispatchMessage(&Message);
            continue;
        }    
        
        // Clear screen.
        
        ClearScreen(0x333333);
        
        // Draw white pixel at 100, 100 (from top left).
        
        DrawPixel(100, 100, 0xffffff);
        
        // Display image.
        
        StretchDIBits(DeviceContext, 0, 0, ClientWidth, ClientHeight, 0, 0, ClientWidth, ClientHeight, Memory, &BitmapInfo, DIB_RGB_COLORS, SRCCOPY);
    }
    
    return 0;
}