Drawing adjacent texture mapped rectangles in OpenGL

I'm drawing a number of texture-mapped rectangles which are sat on top of each other using the following code:

glBegin(GL_QUADS);
glTexCoord2f(0.0, 1.0); glVertex3f(x, y, 0);
glTexCoord2f(0.0, 0.0); glVertex3f(x, y + dy, 0);
glTexCoord2f(1.0, 0.0); glVertex3f(x + dx, y + dy, 0);
glTexCoord2f(1.0, 1.0); glVertex3f(x + dx, y, 0);
glEnd();

This renders correctly at full size, but when I resize it with glScale, single-pixel gaps appear in between some of the rectangles.

However, if I remove the texture map, the rectangles always abut each other correctly.

开发者_如何学编程

What's going wrong, and how can I fix this?

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How does the texture look like? Maybe you've to use a different clamping mode, depending on the texture's contents.

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First of all, make sure they are really gaps, and not texture artifacts, by not using any alpha channel (assuming you were) and picking a background color that stands out like a sore thumb.

Even though you pinpointed texturing as the root cause, a much more likely culprit is rounding errors in the vertex coordinates. Rasterization of adjacent triangles is only guaranteed to be gap-free if the vertex coordinates used match 100%. In stead of calculating them on the fly (x + dx, y + dy), why not store them in an array and make sure you re-use the same coordinates?

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I'm an idiot. The images I was using actually had a transparent row of pixels along the top and bottom.

The original "full-size" rendering was already resizing the texture, and it was a pure fluke that resizing artifacts caused the transparent rows not to be displayed in this case.

Then when I resized the whole lot again with glScale some of the artifacts must have disappeared, and the transparent pixels appeared as gaps.