diff options
| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2019-06-15 14:52:20 +0000 |
|---|---|---|
| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2019-06-15 14:52:20 +0000 |
| commit | 1df50958a6f3bd1ac849b03b44bb4ac00399f446 (patch) | |
| tree | 4ace40c568c1ac49bc9f32ba7ee83b7820338aa3 | |
| parent | 43a6ee392cde1322e645a0e907c604ad0e4cdbbf (diff) | |
| download | netpbm-mirror-1df50958a6f3bd1ac849b03b44bb4ac00399f446.tar.gz netpbm-mirror-1df50958a6f3bd1ac849b03b44bb4ac00399f446.tar.xz netpbm-mirror-1df50958a6f3bd1ac849b03b44bb4ac00399f446.zip | |
miscellaneous update
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@3630 9d0c8265-081b-0410-96cb-a4ca84ce46f8
| -rw-r--r-- | pamtris.html | 49 | ||||
| -rw-r--r-- | pbmpage.html | 4 |
2 files changed, 24 insertions, 29 deletions
diff --git a/pamtris.html b/pamtris.html index f70ff894..7a8f7492 100644 --- a/pamtris.html +++ b/pamtris.html @@ -4,7 +4,7 @@ <body> <h1>pamtris</h1> -Updated: 02 October 2018 +Updated: 15 June 2019 <br> <a href="#index">Table Of Contents</a> @@ -256,14 +256,14 @@ to produce a picture of NAMCO's Pac-Man. It generates dozens of #define WIDTH 256 #define HEIGHT WIDTH -int main() +int main(void) { int const center_x = 0.5 * WIDTH; int const center_y = 0.5 * HEIGHT; double const radius = 0.48 * WIDTH; - int const sectors = round(0.125 * PI * radius) + 1; + int const sectors = round(0.125 * PI * radius + 1); puts("mode triangles"); @@ -277,13 +277,13 @@ int main() printf("vertex %d %d 1\n", center_x, center_y); puts("attribs 255 128 0"); - double const angle_factor = PI2 / (sectors - 1); + double const angle_step = PI2 / (sectors - 1); unsigned int i; for (i = 0; i < sectors; i++) { - double const angle = angle_factor * i; + double const angle = angle_step * i; int const x = round(cos(angle) * radius + center_x); int const y = round(sin(angle) * radius + center_y); @@ -301,7 +301,7 @@ int main() what else can be feasibly obtained through this meta-programming approach, especially when combining <b>pamtris</b> with other Netpbm programs (Earth texture from -<a href="https://visibleearth.nasa.gov/view.php?id=73580">nasa.gov</a>): +<a href="https://visibleearth.nasa.gov/view.php?id=73580">nasa.gov</a>):</p> <img alt="Isometric Rainbow Waves" src="pamtris_isowaves.gif"> <img alt="Rotating Earth" src="pamtris_earth.gif"> @@ -538,11 +538,11 @@ X-axis goes from left to right, and the Y-axis from top to bottom. A negative value for <i>x</i> indicates a column that many tuples to the left of the leftmost column of the frame buffer. Likewise, a negative value for <i>y</i> indicates a row that many tuples above the uppermost -row of the frame buffer. <u>Observe that those coordinates correspond +row of the frame buffer. Observe that those coordinates correspond directly to a particular point in the coordinate system delineated above, regardless of whether you are trying to draw an image which is supposed to look as if viewed "in perspective" or not; <b>pamtris</b> -does <i>not</i> "warp" the coordinates you give in any way.</u> +does <em>not</em> "warp" the coordinates you give in any way. Therefore, if you want to draw images in perspective, you must compute values for <i>x</i> and <i>y</i> already projected into <b>pamtris</b>' coordinate system yourself, using an external perspective projection @@ -573,13 +573,13 @@ intended to look as in perspective is as follows. First, consider the <a href="https://en.wikipedia.org/wiki/Viewing_frustum">typical model</a> of the so-colled "viewing frustum" used to project vertices in 3D "world space" onto a planar "image space." The value of <i>w</i> for a -vertex is simply the dot product<a href="#vertex_note">*</a> between the -3D vector <b>r</b> and the 3D unit vector <b>n</b> (i. e. the length of -the orthogonal projection of <b>r</b> on the line determined by <b>n</b>), -in world units (such as pixels, centimeters, inches, etc.); where -<b>r</b> is the vector which goes from the projection reference point -(PRP, or "eye") to the vertex, and <b>n</b> is just the view-plane -normal (VPN) of unit length which points away from the PRP.</p> +vertex is simply the +<a id="vertex_note_link" href="#vertex_note">dot product*</a> between the 3D +vector <b>r</b> and the 3D unit vector <b>n</b> (i.e. the length of the +orthogonal projection of <b>r</b> on the line determined by <b>n</b>) in +pixels; where <b>r</b> is the vector which goes from the projection reference +point (PRP, or "eye") to the vertex, and <b>n</b> is a view-plane normal +(VPN) of unit length which points away from the PRP.</p> <p>In case you are performing a mere multiplication of a 4D vector with x, y, z and w components by a so-called perspective projection 4x4 matrix @@ -587,7 +587,7 @@ in order to compute the projection of a vertex onto the image plane, then you may supply for <i>w</i> a value which is directly proportional to the absolute value of the w component of the resulting vector.</p> -<p><a id="vertex_note" href="#vertex_note">*</a> +<p>[<a id="vertex_note" href="#vertex_note_link">*</a>]: For any two 3D vectors <b>a</b> and <b>b</b>, with respective real scalar components a<sub>x</sub>, a<sub>y</sub>, a<sub>z</sub> and b<sub>x</sub>, b<sub>y</sub>, b<sub>z</sub>, the dot product between @@ -681,9 +681,8 @@ successfully. If that happens, no lines of input will be read anymore and <b>pamtris</b> will be terminated as if the <b>quit</b> command was given.</p> <dt><b>quit</b></dt> <dd> -<p>This terminates <b>pamtris</b>. The program will not read any more lines of -input after this command, and ignores any further tokens on the -same line as it.</p> +<p>This terminates <b>pamtris</b>. It will not read any more lines of input +after this command.</p> </dd> </dl> @@ -700,17 +699,13 @@ processing the result through <a href="pamlookup.html"><b>pamlookup</b></a>, providing the desired texture file as a "lookup table." If you are drawing pictures in perspective, make sure to provide adequate values for the <i>w</i> parameter to your vertex commands -(<a href="#cmd_vertex">see above</a>) so the resulting samples in +(<a href="#cmd_vertex">see above</a>) so that the resulting samples in the images produced by <b>pamtris</b> are perspective-correct.</p> <p>You might want to consider using <a href="pnmtile.html"><b>pnmtile</b></a> to make textures which are inteded to be "repeated" along triangle meshes.</p> -<p>Since the <i>w</i> parameter to the <b>vertex</b> command was new in Netpbm -10.85 (December 2018), it is not really possible to achieve -perspective-correct texturing before that. - <h3>Anti-aliased edges</h3> @@ -719,9 +714,9 @@ However, it is possible to obtain anti-aliased images through a "super-sampling" approach: draw your image(s) at a size larger than the desired final size, and then, when all post-processing is done, down-scale the final image(s) to the desired size. Drawing images with -twice the desired width and height, then down-scaling them to the -desired size using a quadratic filter, might produce results which are -often good enough.</p> +twice the desired width and height, then down-scaling them to the intended +size while disregarding gamma (i.e. what <b>pamscale -linear</b> does) +often produces good enough results.</p> <h2 id="seealso">SEE ALSO</h2> diff --git a/pbmpage.html b/pbmpage.html index 5e4e2918..6bd44430 100644 --- a/pbmpage.html +++ b/pbmpage.html @@ -2,7 +2,7 @@ <HTML><HEAD><TITLE>Pbmpage User Manual</TITLE></HEAD> <BODY> <H1>pbmpage</H1> -Updated: 01 May 2000 +Updated: 08 June 2019 <BR> <A HREF="#index">Table Of Contents</A> @@ -62,7 +62,7 @@ exact center of the page. <DD> Two diagonal line segments, one starting at the upper left corner of the -page, the other starting from the lower left corner of the page. Both +page, the other starting from the lower right corner of the page. Both extend 1/2" toward the center of the page at 45 degrees. </DL> |