Component: GPU
==============
This is the component provided by [[item:graphics_card|graphics cards]]. For simple programs the [[api:term|term API]] is usually all you need. For more complex operations, or to get a bit more performance, you may wish to interact with the GPU directly, though.

As of OC 1.3 screens of tier 2 and 3 have a 16 color palette. The palette is used to determine the exact colors used when displaying an RGB color.

For tier two this palette contains all colors the screen can possibly display, and is initialized to the standard Minecraft colors. As a side-effect you can specify the colors using `gpu.setBackground(colors.red, true)`, for example. Keep in mind **this only works on tier two screens**. 
Tier three also has an editable 16 color palette, and also a 240 color fixed palette. The editable palette is initialized to grayscale values. The remaining 240 colors are stored as truncated RGB values as was the case in older versions of OpenComputers.

Component name: `gpu`.  
Callbacks:

- [[component:gpu#video_ram_buffers|Video Ram Buffers]]
  This list of component api is getting long, so the new video ram api is listed below on this page in its own section
  - New in OC 1.7.5 Developer builds and expected in the next release (OC 1.8)
- `bind(address: string[, reset: boolean=true]): boolean[, string]`  
  Tries to bind the GPU to a screen with the specified address. Returns `true` on success, `false` and an error message on failure. Resets the screen's settings if reset is 'true'.
  A GPU can only be bound to one screen at a time. All operations on it will work on the bound screen. If you wish to control multiple screens at once, you'll need to put more than one graphics card into your computer.
- `getScreen():string`  
  Get the address of the screen the GPU is bound to. Since 1.3.2.
- `getBackground(): number, boolean`  
  Gets the current background color. This background color is applied to all "pixels" that get changed by other operations.  
  Note that the returned number is either an RGB value in hexadecimal format, i.e. `0xRRGGBB`, or a palette index. The second returned value indicates which of the two it is (`true` for palette color, `false` for RGB value).
- `setBackground(color: number[, isPaletteIndex: boolean]): number[, index]`  
  Sets the background color to apply to "pixels" modified by other operations from now on. The returned value is the old background color, as the actual value it was set to (i.e. not compressed to the color space currently set). The first value is the previous color as an RGB value. If the color was from the palette, the second value will be the index in the palette. Otherwise it will be `nil`.
  Note that the color is expected to be specified in hexadecimal RGB format, i.e. `0xRRGGBB`. This is to allow uniform color operations regardless of the color depth supported by the screen and GPU.
- `getForeground(): number, boolean`  
  Like `getBackground`, but for the foreground color.
- `setForeground(color: number[, isPaletteIndex: boolean]): number[, index]`  
  Like `setBackground`, but for the foreground color.
- `getPaletteColor(index: number): number`  
  Gets the RGB value of the color in the palette at the specified index.
- `setPaletteColor(index: number, value: number): number`  
  Sets the RGB value of the color in the palette at the specified index.
- `maxDepth(): number`  
  Gets the maximum supported color depth supported by the GPU and the screen it is bound to (minimum of the two).
- `getDepth(): number`  
  The currently set color depth of the GPU/screen, in bits. Can be 1, 4 or 8.
- `setDepth(bit: number): string`  
  Sets the color depth to use. Can be up to the maximum supported color depth. If a larger or invalid value is provided it will throw an error. Returns the old depth as one of the strings `OneBit`, `FourBit`, or `EightBit`.
- `maxResolution(): number, number`  
  Gets the maximum resolution supported by the GPU and the screen it is bound to (minimum of the two).
- `getResolution(): number, number`  
  Gets the currently set resolution.
- `setResolution(width: number, height: number): boolean`  
  Sets the specified resolution. Can be up to the maximum supported resolution. If a larger or invalid resolution is provided it will throw an error. Returns `true` if the resolution was changed (may return `false` if an attempt was made to set it to the same value it was set before), `false` otherwise.
- `getViewport(): number, number`  
  Get the current viewport resolution.
- `setViewport(width: number, height: number): boolean`  
  Set the current viewport resolution. Returns `true` if it was changed (may return `false` if an attempt was made to set it to the same value it was set before), `false` otherwise. This makes it look like screen resolution is lower, but the actual resolution stays the same. Characters outside top-left corner of specified size are just hidden, and are intended for rendering or storing things off-screen and copying them to the visible area when needed. Changing resolution will change viewport to whole screen.
- <del>`getSize(): number, number`  
  Gets the size in blocks of the screen the graphics card is bound to. For simple screens and robots this will be one by one.</del> Deprecated, use `screen.getAspectRatio()` instead.
- `get(x: number, y: number): string, number, number, number or nil, number or nil`  
  Gets the character currently being displayed at the specified coordinates. The second and third returned values are the fore- and background color, as hexvalues. If the colors are from the palette, the fourth and fifth values specify the palette index of the color, otherwise they are nil.
- `set(x: number, y: number, value: string[, vertical:boolean]): boolean`  
  Writes a string to the screen, starting at the specified coordinates. The string will be copied to the screen's buffer directly, in a single row. This means even if the specified string contains line breaks, these will just be printed as special characters, the string will not be displayed over multiple lines. Returns `true` if the string was set to the buffer, `false` otherwise.  
  The optional fourth argument makes the specified text get printed vertically instead, if `true`.
- `copy(x: number, y: number, width: number, height: number, tx: number, ty: number): boolean`  
  Copies a portion of the screens buffer to another location. The source rectangle is specified by the `x`, `y`, `width` and `height` parameters. The target rectangle is defined by `x + tx`, `y + ty`, `width` and `height`. Returns `true` on success, `false` otherwise.
- `fill(x: number, y: number, width: number, height: number, char: string): boolean`  
  Fills a rectangle in the screen buffer with the specified character. The target rectangle is specified by the `x` and `y` coordinates and the rectangle's `width` and `height`. The fill character `char` must be a string of length one, i.e. a single character. Returns `true` on success, `false` otherwise.  
  Note that filling screens with spaces (` `) is usually less expensive, i.e. consumes less energy, because it is considered a "clear" operation (see config).

Example use:
```lua
local component = require("component")
local gpu = component.gpu -- get primary gpu component
local w, h = gpu.getResolution()
gpu.fill(1, 1, w, h, " ") -- clears the screen
gpu.setForeground(0x000000)
gpu.setBackground(0xFFFFFF)
gpu.fill(1, 1, w/2, h/2, "X") -- fill top left quarter of screen
gpu.copy(1, 1, w/2, h/2, w/2, h/2) -- copy top left quarter of screen to lower right
```

GPU Color Depth
==============

Color Depth (see `gpu.setDepth` and `gpu.getDepth`) can be 1, 4, or 8 bits separately for foreground and background. These depths provide 2, 16, and 256 colors respectively.

The color value (the `number` passed to `gpu.setBackground` and `gpu.setForeground`) is interpreted either as a 8 bits per channel rgb value (24 bit color) or a palette index.

RGB Color
-----------
The background and foreground colors, as set by calling `setBackground` and `setForeground`, are defined by a `value` (number) and `is_palette` (boolean) pair (the boolean being optional).

When `is_palette` is false (or `nil`), `value` is interpreted as a 24 bit rgb color (0xRRGGBB), regardless of depth. However, the color is approximated to the closest available color in the given depth. In monochrome, zero rounds to zero and all nonzero values round to 1 (and the configured monochrome color is used). In 4 bit color, the closest available color in the palette is selected. In 8 bit color the closest color of the available 256 colors is used. The available 256 colors are described in the following table:

{{:api:oc-256-color.png?nolink&768|}}

Image by [Eunomiac](https://oc.cil.li/index.php?/topic/442-colors-what-determines-colors-i-code-vs-colors-i-get/)

Palette Color
-----------
When `is_palette` is `true`, `value` is interpreted as palette index [0, 16). If you switch from a higher bit density to monochrome note that the color value from the palette is used to determine zero vs the nonzero monochrome color. It is an error to specify a paletted color (i.e. an index value and `true`) in 1 bit depth.

Changing Depth
-----------

Note that the original color pair (the value `number` and palette `bool`) are preserved (background and foreground each) even when switching bit depths. The actual rendering on the screen will update to respect the new depth, but the original 24bit rgb value (or palette index) is not lost. For example, calling `gpu.getBackground` while in 1 bit mode will return the original 24 bit rgb value specified from any previous color depth.


Video Ram Buffers
==============

A GPU card has internal memory that you can allocate into pages. You can specify a custom page size (width and height each must be greater than zero). The total memory of a GPU is reduced by the width*height of an allocation. Each tier of gpu has more total memory than the last. Each page buffer acts like an offscreen [[component:screen|Screen]] with its own width, height, and color. The max color depth of a gpu buffer is based on the gpu tier. Rebooting a machine releases all bufffers.

Each page buffer has its own index; the gpu finds the next available index. Index zero (0) has a special meaning, it is reserved for the screen. Whether a gpu is bound to a screen or not, you can allocate pages, set them active, and read/write to them. Attaching and detaching a screen, even binding to a new screen, does not release the gpu pages. When a computer shuts off or reboots, the pages are released. Each GPU has its own video memory and pages.

Budget and Energy Costs
-----------

Updates to vram (set, copy, fill, etc) are nearly free. They have no energy cost and no additional budget cost. Every direct component invoke (and these gpu methods are direct) has a tiny system minimum budget cost, but the gpu itself in these vram updates adds no additional cost. When bitblt'ing the vram to the screen there is some cost, similar to how updates to the screen normally incur a cost. A dirty (modified) vram back buffer has a one time budget cost that increases with the size of the source buffer. Subsequent bitblts from a clean back buffer to the screen have extremely low costs.

- `getActiveBuffer(): number`  
  Returns the index of the currently selected buffer. 0 is reserved for the screen, and may return 0 even when there is no screen
- `setActiveBuffer(index: number): number`  
  Sets the active buffer to `index`. 0 is reserved for the screen and can be set even when there is no screen. Returns nil for an invalid index (0 is valid even with no screen)
- `buffers(): table`  
  Returns an array of all current page indexes (0 is not included in this list, that is reserved for the screen).
- `allocateBuffer([width: number, height: number]): number`  
  Allocates a new buffer with dimensions width*heigh (gpu max resolution by default). Returns the index of this new buffer or error when there is not enough video memory. A buffer can be allocated even when there is no screen bound to this gpu. Index 0 is always reserved for the screen and thus the lowest possible index of an allocated buffer is always 1.
- `freeBuffer([index: number]): boolean`  
  Removes buffer at `index` (default: current buffer index). Returns true if the buffer was removed. When you remove the currently selected buffer, the gpu automatically switches back to index 0 (reserved for a screen)
- `freeAllBuffers()`  
  Removes all buffers, freeing all video memory. The buffer index is always 0 after this call.
- `totalMemory(): number`  
  Returns the total memory size of the gpu vram. This does not include the screen.
- `freeMemory(): number`  
  Returns the total free memory not allocated to buffers. This does not include the screen.
- `getBufferSize([index: number]): number, number`  
  Returns the buffer size at `index` (default: current buffer index). Returns the screen resolution for index 0. Returns nil for invalid indexes
- `bitblt([dst: number, col: number, row: number, width: number, height: number, src: number, fromCol: number, fromRow: number])`  
  Copy a region from buffer to buffer, screen to buffer, or buffer to screen.
  Defaults:
  * dst = 0, the screen
  * col, row = 1,1
  * width, height = resolution of the destination buffer
  * src = the current buffer
  * fromCol, fromRow = 1,1
  bitblt should preform very fast on repeated use. If the buffer is dirty there is an initial higher cost to sync the buffer with the destination object. If you have a large number of updates to make with frequent bitblts, consider making multiple and smaller buffers. If you plan to use a static buffer (one with few or no updatse), then a large buffer is just fine.
  Returns true on success
  

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