使用OpenGL ES在iOS上绘制细线

Question

I'm trying to draw a 1 pixel width line on iOS, using OpenGL and I faced a problem.

That's how drawn line (zoomed) looks like in simulator:

iPhone 4S

iPhone 6 Plus

As you can see, line is more then 1 pixel width and also it's smoothed. I think, that problem is not in OpenGL, but in screen scale factor. I want that the line is a one-pixel on all types of screens.

That's how I draw the line

- (void)drawView {
    [EAGLContext setCurrentContext:context];

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glViewport(0, 0, backingWidth, backingHeight);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glDisable(GL_LINE_SMOOTH);
    glDisable(GL_BLEND);
    glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f);

    glMatrixMode(GL_MODELVIEW);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    GLfloat vertices[4];
    vertices[0] = -0.5;
    vertices[1] = 0;
    vertices[2] = 0.5;
    vertices[3] = 0;

    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(1.0f, 1.0f, 0.0f, 1.0f);
    glLineWidthx(1.0f);

    glDrawArrays(GL_LINE_STRIP, 0, 2);

    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}

Answer 1

Have a look at http://oleb.net/blog/2014/11/iphone-6-plus-screen/

This shows that the iPhone 6 Plus uses a scaling factor and says that you can disable the scaling by "set the contentScaleFactor of your GLKView to the value of UIScreen.nativeScale"

Hopefully that will fix your problem