I made a program to select color and converted RGB into HEX for color palette in real time. The color result on color palette showed different than a color I selected on OpenGL window. I wasn''t sure what was wrong with it. So I tested my painter program from vendor. I zoomed the picture and selected a color. I still get the same result. Is my computer color blind? Waldoo

Maybe the paint program uses BGR?

Windows bitmaps are BGR, not RGB...
for example, the following code ripped off form the OpenGL superbible would draw a windows bitmap at the current raster position:

glDrawPixels(width, height, GL_BGR, GL_UNSIGNED_BYTE, BitmapBits);

If for some reason you''re using OpenGL prior to 1.2, the colorspace is called GL_BGR_EXT instead of GL_BGR.

Or you can just switch the B and G bytes when putting them into your palette.

I tried your suggestion and it did not work. RGB was more close to accurate color matching. BGR was more like negative color film.

Here is a copy below of color picking function for Visual Basic. I hope you will help solve it.

Waldoo


Private Red As Byte
Private Green As Byte
Private Blue As Byte

Public mousexpos As String
Public mouseypos As String
Option Explicit

Public Function DrawGLScene() As Boolean

glReadPixels mousexpos, mouseypos, 1, 1, rpRed, pxlByte, Red
Form2.Text1(4).Text = Red
glReadPixels mousexpos, mouseypos, 1, 1, rpGreen, pxlByte, Green
Form2.Text1(5).Text = Green
glReadPixels mousexpos, mouseypos, 1, 1, rpBlue, pxlByte, Blue
Form2.Text1(6).Text = Blue

form1.Picture1.BackColor = RGB(Blue, Green, Red)

I just found what the problem was. glReadPixel was reading pixels the glwindow as it was upside down upon window''s mouse coordinate value as the starting point (0,0) is at top left. It is my guess that glReadPixel''s starting point was bottom left or right.

What would you suggest to fix that?

Waldoo

if it starts at the top left and openGL starts at the bottom left... then all you have to do is subtract the given Y value from the height of your window...

if the height is 200, and windows returns 79... what this really means is that the color being picked is 79 from the top of the window or 121 from the bottom... so 200 - 79 = 121.

Jason

"Wise men talk because they have something to say; fools talk because they have to say something." -Plato
http://www.jasontconnell.com

Ya I got it figured out. It was Xposition, (WindowsHeight - Yposition) for the coordinate with windows mouse and glReadPxel.

Anyway the color palette show little darker than the color in glwindow. Do you have any idea why it happened?

Waldoo