texure mapping anti-alias

[fireman2]

I have an 512 by 512 image like this:

I mapped it to a 3D plane:

The location and perspective are all correct. But you can see that the edge is very jigsaw. Does not Open GL has anti-alias or I just did not turn it on?

I am on iPhone ios.

Here is my code:

      CGContextRef spriteContext = CGBitmapContextCreate(spriteData, spriteWidth, spriteHeight, 8, spriteWidth * 4, CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast);

    CGContextTranslateCTM(spriteContext, 0, spriteHeight);

    CGContextScaleCTM(spriteContext, 1, -1);

      CGContextDrawImage(spriteContext, CGRectMake(0.0, 0.0, (CGFloat)spriteWidth, (CGFloat)spriteHeight), spriteImage);

      CGContextRelease(spriteContext);



    glDeleteTextures(1, &spriteTexture);

    glGenTextures(1, &spriteTexture);

    // Bind the texture name. 

    glBindTexture(GL_TEXTURE_2D, spriteTexture);

    // Set the texture parameters to use a minifying filter and a linear filer (weighted average)

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
   glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_FILTER, GL_LINEAR);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );



    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, spriteWidth, spriteHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);

 glClearColor(.0f, 0.0f, 0.0f, .0f);

 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);



 //Setup model view matrix

 glMatrixMode(GL_MODELVIEW);



GLfloat teapot_vertices1[12];




glLoadMatrixf(m);





teapot_vertices1[0] = frames;

teapot_vertices1[1] = frameh;

teapot_vertices1[2] = 0;

teapot_vertices1[3] = frames + framel;;

teapot_vertices1[4] = frameh;

teapot_vertices1[5] = 0;

teapot_vertices1[6] = 0;

teapot_vertices1[7] = 0;

teapot_vertices1[8] = 0;

teapot_vertices1[9] = framel;

teapot_vertices1[10] = 0;

teapot_vertices1[11] = 0;







glVertexPointer(3 ,GL_FLOAT, 0, teapot_vertices1);






for(int i = 0; i < num_teapot_indices; i += new_teapot_indicies[i] + 1)

 {

      glDrawElements(GL_TRIANGLE_STRIP, new_teapot_indicies[i], GL_UNSIGNED_SHORT, &new_teapot_indicies[i+1]);

 }





//glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);



 glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);

 [context presentRenderbuffer:GL_RENDERBUFFER_OES];

[malexander]

Linear interpolation doesn’t produce good antialiasing of textures when the texture is much larger than the screen area it covers. Mipmapping is a better approach. Try creating several mip layers for the texture and set the min filter to GL_LINEAR_MIPMAP_LINEAR (trilinear filtering).

[fireman2]

I tried your approach and now the edge inside is much better:

But the border edge is still jigsaw. Any way we can fix this?

thank you very very much for your help.

Fireman

[malexander]

Multisampling smooths out edges of geometry. I’m not sure what modes are available on iOS, but you need a framebuffer with multiple samples, or a multisample renderbuffer/texture with an FBO. Then call glEnable(GL_MULTISAMPLE) before drawing your geometry. This does cause more of a performance hit than trilinear filtering, however.