In a computer system including a video subsystem, a method for storing and displaying a power on graphical image, comprises the steps of: storing a compressed graphical image in a programmable read-only memory (PROM); initializing a power-on self test (POST); decompressing the compressed graphical image;loading the decompressed graphic image into a random access memory (RAM); and displaying the graphical image during the POST. Also in accordance with another aspect of the invention, a method for adding a user selected graphic image to a system ROM image, comprises the steps of: searching the Flash image file for the graphical image signature (GIS); locating the actual graphical image data with the graphical image header; reading the new graphical image data; overlaying the old graphical image data into a Flash image file; and recalculating the system ROM checksum.

A method and apparatus for shading and texturing 3-dimensional computer generated images deals with punch through textures by supplying data defining a group of surfaces representing each object in the image. For each elementary area of the display, a depth value is generated for each surface of each object in dependence on the distance of that surface from an image plane. Shading and texture data is applied to the surfaces. A determination is made as to whether or not any texture applied to a surface is fully opaque. The depth values are stored for opaque textures at the appropriate elementary areas. The depths of surfaces from subsequent objects are then compared with depth values for the opaque objects at elementary areas and, surfaces or subsequent objects for elementary areas which have a fully opaque surface closer to the image plane than the surface being considered are discarded.

The present invention includes an integrated resize engine and color compare logic for performing a resize bit block transfer (BitBLT) and a transparency BitBLT in a single operation. A source array of pixels is stretched and/or shrunk based upon control signals. The resized pixel values include red, green, and blue color values which are compared with predetermined color range values stored in register pairs. Preferably a register pair is provided for each color. A set of comparators is provided for each color to compare the register values with the color pixel values and to produce an output signal (IN RANGE) indicating if the color pixel value is within the range established by the register values. Each of the in range signals is provided to multiplex logic which generates a transparency enable (TE) output signal based upon the value of the IN RANGE signals and the value of a SELECT input signal. The transparency (TE) signal is written to a dedicated bit in a pixel value register to embed the transparency enable bit as part of the pixel value. Alternatively, or in addition to the multiplex logic, mask logic may be provided to mask the pixel based upon the IN RANGE output signals.

A system and method of rendering overlapping layers in a computer display, such as a windowing system, employs front-to-back assembly of the displayed image. An arbitrary number of overlapping elements, such as windows, can be presented, without requiring temporary storage space or additional off-screen buffers. The front-to-back assembly technique minimizes the number of memory transfers performed in connection with rendering an image, and avoids unnecessary reading and processing of pixels that will not contribute to the final image. Special effects such as semi-transparency, shadows, and irregular shapes can be accommodated and processed in an efficient manner.

A system and method of rendering overlapping layers in a computer display, such as a windowing system, employs front-to-back assembly of the displayed image. An arbitrary number of overlapping elements, such as windows, can be presented, without requiring temporary storage space or additional off-screen buffers. The front-to-back assembly technique minimizes the number of memory transfers performed in connection with rendering an image, and avoids unnecessary reading and processing of pixels that will not contribute to the final image. Special effects such as semi-transparency, shadows, and irregular shapes can be accommodated and processed in an efficient manner.