Depth Buffer Method in Computer Graphics
Depth buffer method, also known as z-buffering, is a fundamental technique used in computer graphics for rendering three-dimensional scenes. It addresses the challenge of determining which objects in a scene are visible and which are obscured by other objects closer to the viewer.
In simple terms, depth buffering involves maintaining a buffer (typically called the depth buffer or z-buffer) that stores the depth of each pixel in the scene. The depth value represents the distance from the viewer to the object at that pixel. When rendering a scene, objects are drawn one by one, and for each pixel, the depth buffer is consulted to determine if the current object is closer to the viewer than any previously drawn objects at that pixel location.
If the depth of the current object is less (i.e., closer) than the depth stored in the depth buffer for that pixel, the current object is considered visible, and its color is written to the frame buffer. The depth buffer is then updated with the depth of the current object. If the depth of the current object is greater (i.e., farther) than the depth in the depth buffer, it means that another object is closer to the viewer, and the current object is occluded and not drawn.
This process ensures that objects farther away from the viewer are occluded by objects closer to the viewer, resulting in a correct depiction of the scene's depth perception. Depth buffering is essential for rendering realistic scenes with proper occlusion and depth ordering.
Example:
Suppose we have a simple scene with three objects: a red cube, a green sphere, and a blue cone. The cube is closest to the viewer, followed by the sphere and then the cone.
During rendering, the depth buffer is initialized with large depth values (e.g., maximum possible depth). As each object is drawn, the depth buffer is checked for each pixel to determine visibility.
When rendering the cube, its depth values are compared with the depth values in the depth buffer. Since the cube is the closest object, its depth values will be smaller than the depth values in the depth buffer for most pixels. Therefore, the cube's color is written to the frame buffer, and the depth buffer is updated with the cube's depth values.
Next, when rendering the sphere, its depth values are compared similarly. Since the sphere is farther away than the cube, its depth values will be greater than the cube's depth values in many pixels. Thus, the sphere will be drawn only where it's not occluded by the cube.
Finally, when rendering the cone, it will be drawn only in areas where neither the cube nor the sphere occludes it.
This process continues until all objects are rendered, ensuring proper occlusion and depth ordering, resulting in a visually accurate representation of the scene.