Intel 815 manual Drawing Characters Using a Font Stored in System Memory

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Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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6.3.2.Drawing Characters Using a Font Stored in System Memory

In this example BLT operation, a lowercase letter “f” is to be drawn in black on a display with a gray background. The resolution of the display is 1024x768, and the graphics system has been set to a color depth of 8 bits per pixel.

Figure 22. On-Screen Destination for Example Character Drawing BLT

(0, 0)

(1023, 0)

128, 128

 

 

Note: Drawing is not to scale

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0

Scan Lines 128 Through 135

20080h

 

 

(128th Scan Lin

 

 

20480h

 

 

(129th Scan Lin

 

 

20880h

128, 128

 

(130th Scan Lin

 

 

 

 

20C80h

 

 

(131th Scan Lin

 

 

21080h

 

 

(132nd Scan Lin

Destination

 

21480h

 

(133rd Scan Lin

 

 

21880h

 

 

(134th Scan Lin

 

 

21C80h

(135, 135)

 

(135th Scan Lin

 

 

135, 135

(0, 767)

(1023, 767)

 

 

 

b_blt12.vsd

The figure above shows the display on which this letter “f” is to be drawn. As shown in this figure, the entire display has been filled with a gray color. The letter “f” is to be drawn into an 8x8 region on the display with the upper left-hand corner at the coordinates (128, 128).

Figure 23. Source Data in System Memory for Example Character Drawing BLT

Source Data

Pixel (0, 0)

Pixel (0, 7)

Pixel (7, 0)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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57 56

48

47

40

39

32 31

24 23

16

15

8

7

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

00000000

00010000

00010000

00111100

00010000

00010000

00001100

00000000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(0, 7)

(7, 7)

 

 

 

 

 

 

 

 

 

 

 

(7, 0)

(0, 0)

Pixel (7, 7)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

b_blt13.vsd

The figure above shows both the 8x8 pattern making up the letter “f” and how it is represented somewhere in the host’s system memory — the actual address in system memory is not important. The letter “f” is represented in system memory by a block of monochrome graphics data that occupies 8 bytes. Each byte carries the 8 bits needed to represent the 8 pixels in each scan line’s worth of this graphics data. This type of pattern is often used to store character fonts in system memory.

During this BLT operation, the host processor will read this representation of the letter “f” from system memory, and write it to the BLT engine by performing memory writes to the ring buffer as an immediate

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Image 66
Intel 815 Drawing Characters Using a Font Stored in System Memory, On-Screen Destination for Example Character Drawing BLT