1. Chapter 8. Drawing Pixels, Bitmaps, Fonts, and Images Computer Graphics (spring, 2009) School of Computer Science University of Seoul

2. Bitmap and Fonts

3. Bitmap ● One bit per pixel. ● “mask” ● Drawing characters. ● Position: glRasterPos*() ● Drawing: glBitmap() ● Example: drawf.cdrawf.c ● Starting from lower-left corner. ● Byte-aligned.

4. Current Raster Position ● Set by glRasterPos*(). ● Transformed by modelview & projection matrices. (not the bitmap!) ● How to position in windows coords? ● To use orthogonal projection & identity modelview. ● To use glWindowPos(). (ver 1.4) – no clipping, etc.

5. Current Bitmap Color ● Set from the current color when glRasterPos*() is called!!! glColor3f(1.0, 1.0, 1.0); /* white */ glRasterPos3fv(position); glColor3f(1.0, 0.0, 0.0); /* red */ glBitmap(....);

6. Images

7. Pitfalls ● OpenGL doesn’t provide features to load/store various image formats. ● OpenGL doesn’t provide any feature related to image compression/decompression.

8. OpenGL Image Manipulation ● glReadPixels(): GPU mem  CPU mem ● glDrawPixels(): CPU mem  GPU mem ● glCopyPixels(): GPU mem  GPU mem

9. glReadPixels() ● GPU mem  CPU mem ● Which buffer to read from? glReadBuffer() ● Pixel format? Table 8-2Table 8-2 ● Pixel type? Table 8-3Table 8-3

10. Pixel Formats & Types ● Bits per pixel determined by the combination. ● For signed formats, negative values not used typically.: less precision. ● Limited valid pixel formats for “packed” types. (ver 1.2) ● GL_*_REV types for MS platform. (ver 1.2)

11. glDrawPixels() ● CPU mem  GPU mem ● Which buffer to write to? glDrawBuffer() ● Example: image.cimage.c

12. glCopyPixels() ● GPU mem  GPU mem ● Which buffer to write from and to? glReadBuffer*() and glDrawBuffer() ● No format and type required.

13. Imaging Pipeline

14. Pixel Packing & Unpacking ● How pixel data is written to and read from the CPU memory. ● Format + type.

15. Pixel-Storage Modes ● Issues ● Subimage ● Big/little endianendian ● Byte alignment ● Set by glPixelStore*().

16. Pixel-Transfer Operations ● Applied to image data while being transferred between CPU & GPU mems. ● Range of components, etc... ● glPixelTransfer*(), glPixelMap*()

17. glPixelZoom() ● Magnifying, reducing, and flipping images for rasterization. ● Example: image.cimage.c

18. Imaging Pipeline ● Fig. 8-4~8 Fig. 8-4~8

19. Reading and Drawing Pixel Rectangles

20. Fig. 8-10 & 11

21. Using Buffer Objects with Pixel Rectangle Data (advanced)

22. Buffer Objects ● OpenGL ver 1.5. ● Pixel data in GPU mem. ● Better performance. ● For advanced effects. ● Example: pboimage.c

23. Tips for Improving Pixel Drawing Rates

24. Imaging Subset (ver 1.2)

25. Imaging Subset ● Color lookup table ● contrast enhancement, filtering, image equalization ● Example: colortable.c ● Convolution ● Replaces each pixel with a weighted average of its neighboring pixels and itself. ● Blurring, sharpening, edge finding, etc. ● Example: convolution.c

26. Imaging Subset ● Color matrix transformation ● Linear transformations on pixel values ● Example: colormatrix.c ● Histogram ● Distribution of color values in an image. ● Example: histogram.c ● Minmax ● min/max pixel component values for a pixel rectangle. ● Example: minmax.c