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NeHe 33 coupled with gluOrtho2D


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#1 Bakuto   Members   -  Reputation: 131

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Posted 03 March 2011 - 10:46 PM

Greetings,

While working with NeHe #33 tutorial, I tried setting glMatrixMode(GL_PROJECTION) with some standard resolutions, (0, 800, 0, 600), etc.
However, when I invoke this call in the init portion of the code, the rotating sprites disappear. I have no idea how what the coordinates correspond to, when rendering the GL_QUADS.

Would anyone be able to show me how to set this up whilst having the glMatrixMode set to GL_PROJECTION?

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#2 radioteeth   Prime Members   -  Reputation: 1104

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Posted 03 March 2011 - 11:22 PM

I do something like this:

void SetPerspective(float fov, float aspect, float znear, float zfar)
{
	float top, bottom, left, right;

	top = znear * tan(fov / 2 * DEG2RAD);
	bottom = -top;
	right = aspect * top;
	left = -right;

	glFrustum(left, right, bottom, top, znear, zfar);
}


void Draw_Perspective()
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	SetPerspective(camera_fov, (float)(app_rect.right - app_rect.left)/(app_rect.bottom - app_rect.top), 1, 99999);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	glRotatef(camera_angles.x, 1, 0, 0);
	glRotatef(camera_angles.y, 0, 1, 0);
	glRotatef(camera_angles.z, 0, 0, 1);
	glTranslatef(-camera_origin.x, -camera_origin.y, -camera_origin.z);
}

void Draw_Ortho()
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0, VID_WIDTH, VID_HEIGHT, 0, -1, 1);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}



The glOrtho takes arguments (left-side, right-side, bottom, top, near, far) it looks like you had it backwards, but that's ok, the OpenGL guys got it backwards IMHO ;)

Oh and to minimize linkage I use glOrtho and glFrustum instead of any glu stuff so that I'm not linking more than is really necessary, but it's really no biggie.

#3 V-man   Members   -  Reputation: 805

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Posted 04 March 2011 - 07:58 AM

gluOrtho2D sets znear to -1 and zfar to 1.0 so perhaps your geometry got clipped.
Sig: http://glhlib.sourceforge.net
an open source GLU replacement library. Much more modern than GLU.
float matrix[16], inverse_matrix[16];
glhLoadIdentityf2(matrix);
glhTranslatef2(matrix, 0.0, 0.0, 5.0);
glhRotateAboutXf2(matrix, angleInRadians);
glhScalef2(matrix, 1.0, 1.0, -1.0);
glhQuickInvertMatrixf2(matrix, inverse_matrix);
glUniformMatrix4fv(uniformLocation1, 1, FALSE, matrix);
glUniformMatrix4fv(uniformLocation2, 1, FALSE, inverse_matrix);




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