Only 2D works.... my 2nd attempt at opengl

OpenGL OpenGL: Basic Coding
1

Ummmm… I drew a triangle in 3D

[ATTACH=CONFIG]278[/ATTACH]

I then changed a z coordinate to be on a different z plane… but it doesnt work?

[ATTACH=CONFIG]277[/ATTACH]

Any ideas please?


#include "frmDeviceRender.h"

void initGL() {
	glClearColor (0.0, 0.0, 0.0, 0.0);
	glColor3f (1.0, 1.0, 1.0);
	glOrtho(0.0, 10.0, 0.0, 10.0, -1.0, 10.0);
};

void drawIt() {
	glClear (GL_COLOR_BUFFER_BIT);
	glBegin(GL_TRIANGLES);
	glVertex3f (2.5, 2.5, 8);
	glVertex3f (7.5, 2.5, 0.0);
	glVertex3f (7.5, 7.5, 0.0);
	glEnd();
	glFlush();
};

void FrmDeviceRender::populateForm() {
	hdc = GetDC (me) ;
	
	GLsizei width = 200;
	GLsizei height = 200;
	int bits = 32;
	GLuint		PixelFormat;
	static	PIXELFORMATDESCRIPTOR pfd=
	{
		sizeof(PIXELFORMATDESCRIPTOR),	// Size Of This Pixel Format Descriptor
		1,								// Version Number
		PFD_DRAW_TO_WINDOW |			// Format Must Support Window
		PFD_SUPPORT_OPENGL |			// Format Must Support OpenGL
		PFD_DOUBLEBUFFER,				// Must Support Double Buffering
		PFD_TYPE_RGBA,					// Request An RGBA Format
		bits,							// Select Our Color Depth
		0, 0, 0, 0, 0, 0,				// Color Bits Ignored
		0,								// No Alpha Buffer
		0,								// Shift Bit Ignored
		0,								// No Accumulation Buffer
		0, 0, 0, 0,						// Accumulation Bits Ignored
		16,								// 16Bit Z-Buffer (Depth Buffer)  
		0,								// No Stencil Buffer
		0,								// No Auxiliary Buffer
		PFD_MAIN_PLANE,					// Main Drawing Layer
		0,								// Reserved
		0, 0, 0							// Layer Masks Ignored
	};

	if (!(PixelFormat=ChoosePixelFormat(hdc,&pfd))) {
		MessageBox(NULL,L"Can't Find A Suitable PixelFormat.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
	}

	if(!SetPixelFormat(hdc,PixelFormat,&pfd)) {
		MessageBox(NULL,L"Can't Set The PixelFormat.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
	}

	if (!(hRC=wglCreateContext(hdc))) {
		MessageBox(NULL,L"Can't Create A GL Rendering Context.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
	}

	if(!wglMakeCurrent(hdc,hRC)) {
		MessageBox(NULL,L"Can't Activate The GL Rendering Context.",L"ERROR",MB_OK|MB_ICONEXCLAMATION);
	}
};

void FrmDeviceRender::onPaint() {
	initGL();

	drawIt();
	SwapBuffers(hdc);
}

void FrmDeviceRender::onUnload() {
	ReleaseDC (me, hdc) ;

	PostQuitMessage (0);
};
2

Let’s see how you trasform your eye space to clip space.
With that parameter you have the following projection matrix


left   = 0
right = 10
top = 0
bottom - 10
near = -1
far = 10
projection = 1/5   0    0      -1
             0   1/5    0      -1
             0     0 -2/11  -9/11
             0     0    0       1

Now you don’t have any model view transformation active, so your vertexes are only transformed by the projection matrix and viewport.

cause you send only three coordinates the w is assumed to be 1.0
glVertex3f (2.5, 2.5, 8); -> -0.5 -0.5 -2.27222 1
OOOPS!! The Z is outside the clip space, your triangle is clipped. And today you have learned that the camera look on the -Z axis.
you points will not be clipped if the Z coord is from 1 to -8

3

[QUOTE=Rosario Leonardi;1241819]Now you don’t have any model view transformation active, so your vertexes are only transformed by the projection matrix and viewport.

cause you send only three coordinates the w is assumed to be 1.0
glVertex3f (2.5, 2.5, 8); -> -0.5 -0.5 -2.27222 1
OOOPS!! The Z is outside the clip space, your triangle is clipped. And today you have learned that the camera look on the -Z axis.
you points will not be clipped if the Z coord is from 1 to -8[/QUOTE]

Thanks for this.

In my own/non-OpenGL engine, I use the projection matrix from wikipedias 3D projection page (3D projection - Wikipedia). How can I achieve a similar style view? I know I need to move over to glFrustum… but I am not sure of what values I need to specify.

I would like to get to the point where I have a frustum 1000 wide, 500 high and 1000 deep. I would then like to be able to specify a coordinate in that range (10, 23, 200… say) and have it mapped automatically.

How is this best done.

I have read tutorials online but they are all overwhelmed with gaming-tutorials/translation/animation/other-irrelevant-stuff

Any help is massively appreciated.

4

I guess your non-openGL engine used DirectX or did you wrote a custom API? I never wrote a single line in DirectX but projection matrix are projection matrix.
You can write your own function that compute the projection matrix (is usually better) or use glFrustum.

I would like to get to the point where I have a frustum 1000 wide, 500 high and 1000 deep. I would then like to be able to specify a coordinate in that range (10, 23, 200… say) and have it mapped automatically.

glFrustum specify a perspective projection, so 1000 wide in witch point? At the end? Usually the matrix is specified like that

p/a 0 0 0
0 p 0 0
0 0 -(f+n)/(f-n) -(2fn)/(f-n)
0 0 -1 0

where a is the aspect ratio = width / height
and p is atan(yfov angle / 2)
f = farPlane
n = nearPlane

If you want to use glFrustum the left right… etc are the size of the near plane.

5

[QUOTE=Rosario Leonardi;1241823]I guess your non-openGL engine used DirectX or did you wrote a custom API? I never wrote a single line in DirectX but projection matrix are projection matrix.
[/QUOTE]

Actually, I wrote it using winAPI (MoveToEx, LineTo etc). It’s not very fast (software only) but I included coordinate projection orthographic/perspective, triangle splitting, backface culling, painters algorithm, a zbuffer and a couple of other bits. it only deals with basic shapes, but thats all i needed until now. its NOT for gaming. the speed issues meant i am forced to look into opengl or directx… so i chose opengl :slight_smile:

I build a projection matrix in that (based on wiki page) but i thought (?) opengl would create that for me… if i specified the frustum???

6

the thinnest end