Delphi与OpenGL基础应用问题：窗体未显示预期深色背景

我用Delphi 10.4开发结合OpenGL的基础应用，要在屏幕上绘制2D图像。代码运行无报错，但窗体始终是灰色，没出现预期的深绿色背景。已在IDE和独立程序测试，Windows 10系统，确认System32里有opengl32.dll。请问问题出在哪？

原代码 #

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, OpenGL;

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormResize(Sender: TObject);
  private
    { Private declarations }
    GLContext : HGLRC;
    glDC: HDC;
    errorCode: GLenum;
    openGLReady: Boolean;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  pfd: TPixelFormatDescriptor;
  FormatIndex: Integer;
begin
  FillChar(pfd,SizeOf(pfd),0);
  with pfd do
  begin
    nSize := SizeOf(pfd);
    nVersion := 1; {The current version of the desccriptor is 1}
    dwFlags := PFD_DRAW_TO_WINDOW or PFD_SUPPORT_OPENGL;
    iPixelType := PFD_TYPE_RGBA;
    cColorBits := 24; {support 24-bit color}
    cDepthBits := 32; {depth of z-axis}
    iLayerType := PFD_MAIN_PLANE;
  end;
  glDC := getDC(handle);
  FormatIndex := ChoosePixelFormat(glDC,@pfd);
  SetPixelFormat(glDC,FormatIndex,@pfd);
  GLContext := wglCreateContext(glDC);
  wglMakeCurrent(glDC,GLContext);
  OpenGLReady := true;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  wglMakeCurrent(Canvas.Handle,0);
  wglDeleteContext(GLContext);
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  if not openGLReady then
    exit;
  {background}
  glClearColor(0.1,0.0,0.1,0.0);
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity; // Reset The View
  glTranslatef(0.0, 0, 0.0);
  glRotateF (360, 0.0, 0.0, 1.0);
  glBegin( GL_POLYGON ); // start drawing a polygon
    glColor3f( 1.0, 0.0, 0.0);
    glVertex3f( 0.0, 0.5, 0.0 ); // Top
    glColor3f(0.0, 1.0, 0.0);
    glVertex3f( 0.5, -0.5, 0.0 ); // Bottom Right
    glColor3f(0.0, 0.0, 1.0);
    glVertex3f( -0.5, -0.5, 0.0 ); // Bottom Left
  glEnd;
  glFlush;
  {error checking}
  errorCode:=glGetError;
   if errorCode<>GL_NO_ERROR then
      raise Exception.Create('Error in Paint'#13+gluErrorString(errorCode));
  SwapBuffers(wglGetCurrentDC);
  glFlush();
end;

procedure TForm1.FormResize(Sender: TObject);
begin
  if not openGLReady then
  exit;
  glViewPort(0,0,ClientWidth,ClientHeight);
  glOrtho(-1.0,1.0,-1.0,1.0,-1.0,1.0);
  errorCode := glGetError;
  if errorCode<>GL_NO_ERROR then
  raise Exception.Create('FormResize:'+gluErrorString(errorCode));
end;

procedure GLInit;
begin
  // set viewing projection
  glMatrixMode(GL_PROJECTION);
  glFrustum(-0.1, 0.1, -0.1, 0.1, 0.3, 15.0);
  // position viewer
  glMatrixMode(GL_MODELVIEW);
  glEnable(GL_DEPTH_TEST);
end;

end.

问题分析与修正方案 #

你的代码存在多处细节错误，导致OpenGL绘制内容无法正常显示：

1. 初始化函数未调用
   定义了GLInit用于设置投影矩阵，但从未在FormCreate中调用，导致OpenGL矩阵状态异常，绘制内容不在可视区域。
   修正：在wglMakeCurrent后添加GLInit;调用。

2. 销毁上下文时DC错误
   FormDestroy中使用Canvas.Handle作为DC来释放上下文，应该用创建时保存的glDC，否则会导致上下文清理异常。
   修正：

   procedure TForm1.FormDestroy(Sender: TObject);
   begin
     wglMakeCurrent(glDC, 0);
     wglDeleteContext(GLContext);
   end;
   

3. glViewport拼写错误
   FormResize中的glViewPort是笔误，正确函数名是glViewport（小写p），这个错误会导致视口设置失败，内容无法映射到窗体。
   同时设置glOrtho前需要切换到投影矩阵并重置，否则会叠加之前的矩阵变换：
   修正：

   procedure TForm1.FormResize(Sender: TObject);
   begin
     if not openGLReady then exit;
     glViewport(0,0,ClientWidth,ClientHeight);
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity;
     glOrtho(-1.0,1.0,-1.0,1.0,-1.0,1.0);
     glMatrixMode(GL_MODELVIEW);
     errorCode := glGetError;
     if errorCode<>GL_NO_ERROR then
       raise Exception.Create('FormResize:'+gluErrorString(errorCode));
   end;
   

4. SwapBuffers与glFlush冗余/错误
   FormPaint中重复调用glFlush，且SwapBuffers使用wglGetCurrentDC不如直接用保存的glDC可靠，应该只在交换缓冲区前或后调用一次glFlush。同时要清空深度缓冲区，避免绘制被遮挡：
   修正：

   procedure TForm1.FormPaint(Sender: TObject);
   begin
     if not openGLReady then exit;
     glClearColor(0.1,0.0,0.1,0.0);
     glClear(GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT);
     glLoadIdentity;
     glTranslatef(0.0, 0, 0.0);
     glRotateF (360, 0.0, 0.0, 1.0);
     glBegin( GL_POLYGON );
       glColor3f( 1.0, 0.0, 0.0);
       glVertex3f( 0.0, 0.5, 0.0 );
       glColor3f(0.0, 1.0, 0.0);
       glVertex3f( 0.5, -0.5, 0.0 );
       glColor3f(0.0, 0.0, 1.0);
       glVertex3f( -0.5, -0.5, 0.0 );
     glEnd;
     errorCode:=glGetError;
     if errorCode<>GL_NO_ERROR then
       raise Exception.Create('Error in Paint'#13+gluErrorString(errorCode));
     glFlush;
     SwapBuffers(glDC);
   end;
   

5. 深度缓冲区冲突
   你请求了32位深度缓冲区，且GLInit启用了GL_DEPTH_TEST，但2D绘图不需要深度测试，若为纯2D应用，可以在GLInit中去掉glEnable(GL_DEPTH_TEST)，减少不必要的性能开销。

额外建议 #

• 2D绘图时，GLInit中的glFrustum（透视投影）可以替换为glOrtho（正交投影），更符合2D场景需求。
• 每次矩阵操作后记得切换回GL_MODELVIEW矩阵，避免后续绘制使用错误的矩阵模式。

内容的提问来源于stack exchange，提问作者brane