Painting on an image leaves trail?

s00014405

22y2.5kGDI+

I've been developing an Air Hockey project and i only started using GDI+ I know people told me on here that GDI+ would not be fast enough for this Air Hockey game (and to use C# instead) but i think an element of the project for me will be to test the limits of GDI+. Anyways, i'm a real beginner at GDI+ and i've been looking at a couple of examples and am reading up on it. Back to the point - i'm drawing a puck and paddle on a PictureBox control of a table. And manipulating them according to the mouse movements. Am just working on the paddle right now but am getting a trail when i move the paddle around. How do i clear this trail? I tried using the g.Clear(Color.Transparent) etc. but it's clearing the PictureBox completely. Would i need to use the Invalidate method to do this? This is what i mean by a trail.. http://homepage.eircom.net/~basquilletj/GdiPlusTrail.JPG Any suggestions would be much appreciated! Sample of some of my code below: Thanks in advance! private void frmTable_Paint(object sender, System.Windows.Forms.PaintEventArgs e) { { g = Graphics.FromImage(picTable.Image); gameDraw(); } private void gameDraw() { // all brushes SolidBrush redBrush = new SolidBrush(Color.FromArgb(255,50,50)); Pen blackPen = new Pen( Color.Black, 2 ); Pen bluePen = new Pen( Color.Blue, 2 ); //draw puck g.FillEllipse( redBrush, puck_x, puck_y, 32, 32 ); g.DrawEllipse( blackPen, puck_x, puck_y, 32, 32 ); //draw paddle g.FillEllipse( redBrush, paddle_x, paddle_y, 32, 32 ); g.DrawEllipse( bluePen, paddle_x, paddle_y, 32, 32 ); bluePen.Dispose(); redBrush.Dispose(); blackPen.Dispose(); } private void gameLoop(Object sender, EventArgs e) { if ( paddle_x <= 0 ) x_vel *= -1; if ( paddle_y <= 0 ) y_vel *= -1; //Called so the form will repaint itself. Invalidate(); } private void frmTable_Load(object sender, System.EventArgs e) { gameClock = new Timer(); //Start the game clock to control game speed gameClock.Interval = 15; gameClock.Tick += new EventHandler(gameLoop); gameClock.Start(); // initial dimensions for puck puck_x = 200; puck_y = 200; // initial dimensions for paddle paddle_x = 150; paddle_y = 150; } private void picTable_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e) { paddle_x = e.X-10; paddle_y = e.Y-10; }

10 Replies

Know the answer? Post it — somebody with the same question will find it here.

s0001440522y ago
Making some progress here - the only problem i have now is the puck and paddle i've drawn keep flashing.
bilnaad22y ago
At the beginning of tye method try this; Graphics g = picTable.CreateGraphics();
s0001440522y ago
Still not working, i'm afraid... Am getting no image being loaded at all. See here: http://homepage.eircom.net/~basquilletj/pic1.JPG
bilnaad22y ago
The code: g = Graphics.FromImage(picTable.Image); creates a new graphics object from the image. So it takes the image from the pictable(wich is blank) and updates the Graphics(g) with that image. So when you had done all the drawing you reset the whole thing with the blank picTable image. So just dlete that line please ^_^
bilnaad22y ago
ow sorry, I made a typo ^_^ I adjusted your code so it should work. Just copy/paste private void gameDraw() { g.Clear(Color.White); // all brushes SolidBrush redBrush = new SolidBrush(Color.FromArgb(255,50,50)); Pen blackPen = new Pen( Color.Black, 2 ); Pen bluePen = new Pen( Color.Blue, 2 ); //draw puck g.FillEllipse( redBrush, puck_x, puck_y, 32, 32 ); g.DrawEllipse( blackPen, puck_x, puck_y, 32, 32 ); //draw paddle g.FillEllipse( redBrush, paddle_x, paddle_y, 32, 32 ); g.DrawEllipse( bluePen, paddle_x, paddle_y, 32, 32 ); bluePen.Dispose(); redBrush.Dispose(); blackPen.Dispose(); //---------------------------------------------- //Not needed anymore ^_^ g = Graphics.FromImage(picTable.Image); }
s0001440522y ago
Never mind - got that sorted... The syntax was actually: g.Clear(Color.White); But for some reason, it's leaving the pictureBox as White and isn't updating it with the image i've specified in the last line of the function.
s0001440522y ago
Am getting the error: System.Drawing.Graphics' does not contain a definition for 'Graphics' private void gameDraw() { g.Graphics.Clear(Color.White); // all brushes SolidBrush redBrush = new SolidBrush(Color.FromArgb(255,50,50)); Pen blackPen = new Pen( Color.Black, 2 ); Pen bluePen = new Pen( Color.Blue, 2 ); //draw puck g.FillEllipse( redBrush, puck_x, puck_y, 32, 32 ); g.DrawEllipse( blackPen, puck_x, puck_y, 32, 32 ); //draw paddle g.FillEllipse( redBrush, paddle_x, paddle_y, 32, 32 ); g.DrawEllipse( bluePen, paddle_x, paddle_y, 32, 32 ); bluePen.Dispose(); redBrush.Dispose(); blackPen.Dispose(); g = Graphics.FromImage(picTable.Image); }
bilnaad22y ago
Ah, I think I know it ^_^ At the very beginning of the function call this. g.Graphics.Clear(Color.White); This clears the graphics with the provided color. Should work ^_^
s0001440522y ago
Cheers nobrainer! Owe you one... but not too sure bout the syntax to make a blank image. Tried using Graphics g but doesn't seem to accept 0 arguments... any ideas? I assume what you mean is something like this: private void gameDraw() { // Syntax For Blank Image Here // // all brushes SolidBrush redBrush = new SolidBrush(Color.FromArgb(255,50,50)); Pen blackPen = new Pen( Color.Black, 2 ); Pen bluePen = new Pen( Color.Blue, 2 ); //draw puck g.FillEllipse( redBrush, puck_x, puck_y, 32, 32 ); g.DrawEllipse( blackPen, puck_x, puck_y, 32, 32 ); //draw paddle g.FillEllipse( redBrush, paddle_x, paddle_y, 32, 32 ); g.DrawEllipse( bluePen, paddle_x, paddle_y, 32, 32 ); bluePen.Dispose(); redBrush.Dispose(); blackPen.Dispose(); g = Graphics.FromImage(picTable.Image); }
bilnaad22y ago
Are you just drawing to an image or is the image updated(with an new image). If you just draw to the image the old image will remain and the new elements are drawn on top of it. So it leaves a trail. On gamedraw() start with a blank image and at the end replace the image of picTable with the newly created image.