How do you display a pixel of color C to iPhone coordinates (x, y)?

Question

I've read all Apple documentation on the iPhone development and there's nothing that describes how to do it.

Answer 1

The drawing on iPhone is not pixel-oriented in this way. You can draw a rectangle of size 1x1 using the Quartz API if you want in your drawRect: method:

CGColorRef colorRef = CGColorCreateGenericRGB(r, g, b, a);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, colorRef);
// This next line does the drawing; repeat for as many x,y pairs as you want.
CGContextFillRect(context, CGRectMake(x,y,1,1)); 
CGColorRelease(colorRef);

But you wouldn't want to fill the entire screen using this method, it's crazy slow. You should think in terms of vectors: lines, rectangles, other polygons. This applies to both Quartz (like the above) and OpenGL.

If you really are doing something that ends up rendering pixel-at-a-time filling a whole screen, your best bet may be using Quartz to create an offscreen bitmap context, writing to the bitmap memory directly per-pixel, and then drawing the whole thing to the drawing context inside drawRect:. You could also use OpenGL to draw a series of single-pixel sized GL_POINTs (instead of triangles), which may be faster depending on what you're doing.