Visualization, Spring'98, Yap

LECTURE 5: PIXEL PIPELINE

  1. INTRODUCTION

    OpenGL is justly touted as a 3-D Graphics API, as its 3D geometry pipeline architecture is quite sophisticated. However, OpenGL also provides important support for direct pixel manipulation, bypassing most of this pipeline. We need to understand this alternative pipeline in this course.

  2. BITMAPS and IMAGES

    -- Pixel manipulation operates on two kinds of data arrays:
    • Bitmaps are 0/1 rectangular arrays.
    • Images are basically RGBA-valued rectangular arrays.
    -- The bottom-left corner of such an array is called its origin.
    -- These arrays are stored in row-major order, starting from the origin, from left to right, bottom row to top row.
    -- See [Guide, ch.8] for more details.

  3. CURRENT RASTER POSITION

    -- The OpenGL state includes a current raster position, important for pixel-based commands.
    -- We can specify this position using
    glRasterPos*(x, y, ...)
    E.g.,
    glRasterPos4f(10.0, 20.0, 0.0, 1.0)
    -- When we draw a bitmap or image, the origin of the array will be made to coincide with the current raster position.
    -- More on current raster position

  4. USING BITMAPS

    -- Useful in defining fonts (in conjunction with display lists [Angel, ch.2][Guide, ch.2].
    -- Basic command:
    glBitmap(width, ht, x_0, y_0, x_mov, y_mov, raster)
    -- More details

  5. MANIPULATING IMAGES

    -- THREE BASIC COMMANDS: -- Besides direct display, images are also useful for texture maps.
    -- OTHER USEFUL COMMANDS

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