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Solance

OpenGL Little C++ opengl help please :)

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Could i get a example of how to use this say i have a image drawn like so.
glBegin(GL_QUADS);
				glTexCoord2f(0.0f, 0.0f),		glVertex3f(-1.0f, -1.0f, 0.0f);
				glTexCoord2f(1.0f, 0.0f),		glVertex3f(1.0f, -1.0f, 0.0f);
				glTexCoord2f(1.0f, 1.0f),		glVertex3f(1.0f, 1.0f, 0.0f);
				glTexCoord2f(0.0f, 1.0f),		glVertex3f(-1.0f, 1.0f, 0.0f);
	glEnd();



how would i grab say a 16x16 portion from 32x32 using glCopyTexSubImage2D()? [Edited by - Solance on May 26, 2005 5:32:17 PM]

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I have tried this

glCopyTexSubImage2D(
GL_TEXTURE_2D,
0,
(x - CLIENTHBUF) * TILESIDE,
(y - CLIENTVBUF) * TILESIDE,
0,
0,
TILESIDE,
TILESIDE
);



but all it draws is white... could i get a example of how you guys have used this?

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The simpler and faster method is to use different texture coordinates,
e.g.

// displays the upper left quarter of a given texture
glBegin(GL_QUADS);

glTexCoord2f(0.0f, 0.0f);
glVertex3f(-1.0f, -1.0f, 0.0f);

glTexCoord2f(0.5f, 0.0f);
glVertex3f(1.0f, -1.0f, 0.0f);

glTexCoord2f(0.5f, 0.5f);
glVertex3f(1.0f, 1.0f, 0.0f);

glTexCoord2f(0.0f, 0.5f);
glVertex3f(-1.0f, 1.0f, 0.0f);

glEnd();



HTH,
Pat

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Have you made sure the texure loading routine was successful, and that you have bound it before using glTexCoord with glBindTexture? You could also try disabling any lighting if that's enabled, just to make sure the lighting isn't the problem?

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yes i can draw the texture to the screen fine, but when i draw it the copy just gets white, using x=0 y=0 still just white everything is just white.

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I do not understand what your problem is:

1) Nothing appears but white?

or

2) You want to map a smaller portion of the texture to the quad?


Plese clarify

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Paste all of your code.
Its hard to tell if you're doing something wrong with vauge explinations of 'its not working'

How do you know if your texture loading routine was sucessful if it only draws white. That would lead me to believe that it isn't successful.
The only other thing I can think of is setting your object color to whitebefore you draw. But that only applies in certain situations, blending issues.

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BitmapToTexture(map.m_tileimg, data, nwidth, nheight);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1, &texNamer);
glBindTexture(GL_TEXTURE_2D, texNamer);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(
GL_TEXTURE_2D,
0,
GL_RGBA,
1024,
512,
0,
GL_RGBA,
GL_UNSIGNED_BYTE,
data
);
//delete[] data;
//glBindTexture(GL_TEXTURE_2D, texNamer);
//glClear(GL_COLOR_BUFFER_BIT);

//glClear(GL_BACK);
//glDrawBuffer(GL_BACK);
//glReadBuffer(GL_BACK);
//glBindTexture(GL_TEXTURE_2D, texNamer);
//glBlendFunc(GL_ONE, GL_ZERO);
//glEnable(GL_TEXTURE_2D);
glBegin(GL_QUADS);

glTexCoord2f(0.0f, 0.0f);
glVertex3f(-1.0f, -1.0f, 0.0f);

glTexCoord2f(0.5f, 0.0f);
glVertex3f(1.0f, -1.0f, 0.0f);

glTexCoord2f(0.5f, 0.5f);
glVertex3f(1.0f, 1.0f, 0.0f);

glTexCoord2f(0.0f, 0.5f);
glVertex3f(-1.0f, 1.0f, 0.0f);

glEnd();
delete[] data;

glBindTexture(GL_TEXTURE_2D, tex_map);
glCopyTexSubImage2D(
GL_TEXTURE_2D,
0,
(x - CLIENTHBUF) * TILESIDE,
(y - CLIENTVBUF) * TILESIDE,
0,
0,
TILESIDE,
TILESIDE
);



I know it draws it correctly when i draw the texture to the screen it works fine but when i draw the texture that is being copied it does not work at all just draws white

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well glCopyTexSubImage2D copies from the current gl Read buffer.

also check for errors after every texture call.

your offset might be incorrect.

But glCopyTexSubImage2D is used to replace portions of a texture with pixels in the buffer at the specified locations which im not quite sure if this is what you want. Also post in the openGL forum rather than general programming.

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