![]() Note that most emulators do not show these dots-the above video was taken from the emulator BlastEm. This is most obvious on the scanlines where two palettes are changed at once, near the cockpit displays. At each of these points, there are noticeable CRAM dots. The third point is just above the bottom cockpit display (just below the water). The second point is the horizon-where the sky meets the water. The first point is just below the cockpit display at the top of the screen (just above the sky). Now, re-watch the above video clip and try to identify where the palettes are changed by mentally aligning the diagram with the video. This palette is changed three times in a single frame, at the vertical positions where the colors change in the diagram. The leftmost 16 columns represent the first palette. The vertical position where the color changes on the diagram corresponds to the vertical position of the change on the display. A column with more than one color indicates a mid-frame color change. Each column represents an entry on a color palette. If we map out the color palettes for each horizontal line of the display, we get this:Ī representation of the color palettes in the above Burning Force example. Let’s look at an example of mid-frame palette swapping from Burning Force: Colors are swapped mid-frame several times in this scene from Burning Force. However, sometimes CRAM dots were left as-is. Developers often obscured these dots using sprites, as we will see in some examples below. The more colors written to CRAM at a time, the more CRAM dots will appear. Any time a color is written to CRAM while the screen is being actively rendered, that color will appear on the screen in a single pixel rather than the intended color. One of the tradeoffs to mid-frame palette swapping is that artifacts will often appear on the screen. This technique can be used to surpass the color limitations of the VDP, although it comes with tradeoffs. The process can be repeated more than once per frame. ![]() This raster effect results in one vertical section of the screen being drawn with one set of palettes, while another section is drawn with another set of palettes. Palette colors can be changed in CRAM while the VDP is in the middle of rendering a frame and then changed back at the end of the frame, a process known as mid-frame palette swapping. Return to Table of Contents Palette Swapping ![]()
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