| 0,0 → 1,173 |
|---|
| |
| Implementation detail differences |
| ================================= |
| |
| FilterFoundry tries to be as compatible with Filter Factory as possible. |
| However, results are usually not 100% equal because functions like |
| cos, sin, sqr, etc., have different accuracy due to the underlying |
| implementation. |
| |
| Furthermore, there are the following known differences between |
| Filter Foundry and Filter Factory: |
| |
| i, u, v (Testcase iuv.afs) |
| ------- |
| |
| Filter Foundry <1.7 uses the same formulas as in Filter Factory: |
| |
| i=((76*r)+(150*g)+(29*b))/256 // Output range is 0..254 |
| u=((-19*r)+(-37*g)+(56*b))/256 // Output range is -55..55 |
| v=((78*r)+(-65*g)+(-13*b))/256 // Output range is -77..77 |
| |
| Filter Foundry 1.7 uses more accurate formulas: |
| |
| i=(299*r+587*g+114*b)/1000 // Output range is 0..255 |
| u=(-147407*r-289391*g+436798*b)/2000000 // Output range is -55..55 |
| v=614777*r-514799*g-99978*b)/2000000 // Output range is -78..78 |
| |
| Both formulas follow the same YUV standard but have different accuracy. |
| |
| |
| get(i) (Testcase getput.afs) |
| ------ |
| |
| Filter Foundry: |
| |
| get(x)=0 if x>255 or x<0 |
| |
| Filter Factory: |
| |
| get(x)=x if x>255 or x<0 |
| |
| Note: The result "x" was most likely not intended but a result of an undefined behavior |
| |
| |
| r, g, b at empty canvas (Testcase emptycanvas.afs) |
| ----------------------- |
| |
| In Filter Factory, an empty (transparent) canvas of a new file is initialized as `r=g=b=0` |
| |
| Filter Foundry initializes it as `r=g=b=255` |
| |
| |
| rnd(a,b) and rst(i) (Testcases rst_*.afs) |
| ------------------- |
| |
| Filter Foundry's implementation of rst(i) (an undocumented function that sets the seed for the PRG) |
| and rnd(a,b) (generate a random number between a and b, inclusively) |
| differs from the implementation of Filter Factory in many ways. |
| |
| 1. In Filter Foundry, the random seed is automatically initialized with seed 691204. |
| In Filter Factory, the random seed is automatically initialized with seed 0. |
| |
| 2. In Filter Foundry, the argument i of the function rst(i) is limited to the |
| type "unsigned int" (argument of the function srand() in the C StdLib), |
| so the allowed range is 0..4294967295. |
| |
| In Filter Factory, the argument i must be between 0 and 32767, inclusively. |
| If the argument is not within this range, the operation "and 0x7FFF" will be applied to it |
| to extract the low 15 bits. |
| |
| 3. In Filter Foundry, the function rnd(a,b) retrieves a random number in realtime; therefore, if the |
| seed is changed via rst(i), there is an immediate effect on the next call of the rnd(a,b) function. |
| For example, following filter would generate an one-colored picture without any randomness: |
| R: rst(123), rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255) |
| |
| If you want to generate a random pixel image with a non-default seed, you need to make sure |
| that rst(i) is called only once at the beginning (channel 0, coordinate 0|0): |
| R: (x==0 && y==0) ? rst(123) : 0, rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255) |
| |
| In Filter Factory, the rnd(a,b) function is more complex. |
| As soon as the function rnd(a,b) is used once, rst(i) will not have any effect. |
| So, if you want to use rst(i), you must make sure to call it before using rnd(a,b). |
| Following filter will generate a random pixel picture: |
| R: rst(123), rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255) |
| Following filter would generate a different random pixel picture: |
| R: rst(456), rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255) |
| Following filter would generate the same random pixel picture: |
| R: rst(456), rnd(0,255)+rst(123) // note that rst() always returns 0, so the '+' operator is OK |
| G: rnd(0,255) |
| B: rnd(0,255)+rst(456) // the last rst(456) call is to mitigate a bug; see below. |
| |
| 4. In Filter Factory, due to a bug, the random state is not reset to its initial state (0) before the filter is applied: |
| The preview image processing will modify the random state, and once the filter is actually applied (pressing "OK"), |
| the random state that was set in the preview picture, will be used. |
| Example: |
| R: rnd(0,255), rst(123) // note that the rst(123) is ignored because rnd() was already called. |
| G: rnd(0,255) |
| B: rnd(0,255) |
| This filter will produce a random pixel picture with the initial default random seed 0, |
| but only for the first calculation (i.e. in the preview picture processing, or in a standalone filter without dialog). |
| Any further calculation will result in a random pixel picture with random seed 123, |
| since the random seed 123 will be taken from the previous run. |
| |
| Furthermore, the random state can't be changed again, not even at the beginning of the red channel before any rnd() call. |
| Example: |
| R: rst(333), rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255)+rst(555) |
| This filter will produce a picture with random seed 333 on the first calculation, |
| and at every further calculation, a random picture with seed 555. |
| Another example: |
| R: rst(ctl(0)), rnd(0,255) |
| G: rnd(0,255) |
| B: rnd(0,255)+rst(555) |
| In this filter, the slider value is ignored and the resulting picture will always be the same. |
| |
| |
| Evaluation of conditional branches |
| ---------------------------------- |
| |
| **Filter Foundry:** |
| |
| Only the branches which will be chosen due to the conditional expression will be evaluated. |
| |
| This means that following filter would generate a black canvas: (Testcase conditional_eval_1.afs) |
| |
| R: 1==0 ? put(255,0) : 0 |
| G: get(0) |
| B: 0 |
| |
| In boolean expressions, the evaluation will be aborted if the result is already determined. |
| |
| So, this will also generate a black canvas: (Testcase conditional_eval_2.afs) |
| |
| R: 1==0 && put(255,0) ? 0: 0 |
| G: get(0) |
| B: 0 |
| |
| This will also generate a black canvas: (Testcase conditional_eval_3.afs) |
| |
| R: 1==1 || put(255,0) ? 0 : 0 |
| G: get(0) |
| B: 0 |
| |
| **Filter Factory:** |
| |
| Each branch inside a if-then-else expression will be evaluated. |
| This means that following filter would generate a green canvas: (Testcase conditional_eval_1.afs) |
| |
| R: 1==0 ? put(255,0) : 0 |
| G: get(0) |
| B: 0 |
| |
| Also, all arguments of an boolean expression will be fully evaluated. |
| So, this will also generate a green canvas: (Testcase conditional_eval_2.afs) |
| |
| R: 1==0 && put(255,0) ? 0: 0 |
| G: get(0) |
| B: 0 |
| |
| This will also generate a green canvas: (Testcase conditional_eval_3.afs) |
| |
| R: 1==1 || put(255,0) ? 0 : 0 |
| G: get(0) |
| B: 0 |