Z-slope test to optimize sample throughput

A method for rendering three-dimensional images, the method comprising:

• receiving 3-D graphics data corresponding to a polygon;
• calculating a Z slope using the 3-D graphics data, wherein the Z slope characterizes a rate of change of Z across the polygon;
• determining if the absolute Z slope is less than a threshold value, wherein, if the absolute Z slope is less than the threshold value, then:
• rendering parameter values, using the 3-D graphics data, for all sample positions that are within the polygon and are within a first type of sample bin that intersects an edge of the polygon;
• and
• rendering parameter values, using the 3-D graphics data, for a selected sample position of a plurality of sample positions that are within the polygon and in a second type of sample bin that does not intersect an edge of the polygon, and assigning the same parameter values rendered for the selected sample position to each sample position of the plurality of sample positions.

A graphics system for rendering three-dimensional images, the system comprising:

• an input for receiving 3-D graphics data corresponding to a polygon, wherein the 3-D graphics data includes vertex data;
• a plurality of memories for storing parameter data for samples;
• a render processor coupled to the input and the plurality of memories,
• wherein the render processor is operable to calculate a Z slope, wherein the Z slope characterizes a rate of change of Z across the polygon;
• wherein the render processor is operable to determine if the absolute Z slope is less than a threshold value, and if the absolute Z slope is less than a threshold value, then the render processor is operable to store parameter values rendered for a first sample position selected from a group of neighboring sample positions in memory locations corresponding to two or more of the neighboring sample positions in one or more of the plurality of memories.