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Coloring from black to fully transparent

 
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Ghoti



Joined: 31 Dec 2005
Posts: 288
PostPosted: Wed Aug 23, 2006 10:04 pm    Post subject: Coloring from black to fully transparent Reply with quote
Hi folks,

I want to make a fading thingy that fades from black to transparent.

for this i use the rectangle to screen function (from graphics.c from the yelarb tutorials):

Code:
extern void fillScreenRect(Color color, int x0, int y0, int width, int height);


the color however is not in ABGR, it is in some other format that is only 1 large number. I know that there is some kind of conversion to alter the alpha channels of the color. I have seen in some other posts that they use (i guess) bitshifting. however i don't really know what it is and how i can use it for this problem. The examples i could find only work the other way around. they work from that colorcode to AGBR and i need the other way.

can someone help me out?

greets ghoti
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Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php
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Aion



Joined: 24 Jul 2006
Posts: 40
Location: Montreal
PostPosted: Wed Aug 23, 2006 11:53 pm    Post subject: Reply with quote
That should do the job :

Code:

//Takes value between 0-255 for each channel, output 32bits color
#define ARGB8888(_A_,_R_,_G_,_B_)   (   ((u32)_A_&0xFF)<<24)   |   \
                           (         ((u32)_R_&0xFF)<<16)   |   \
                           (         ((u32)_G_&0xFF)<<8)      |   \
                           (      ((u32)_B_&0xFF)<<0)         )

//Takes value between 0-16 for each channel, output 16bits color
#define ARGB4444(_A_,_R_,_G_,_B_)   (   ((u16)_A_&0x0F)<<12)   |   \
                           (   ((u16)_R_&0x0F)<<8)   |   \
                           (   ((u16)_G_&0x0F)<<4)      |   \
                           (   ((u16)_B_&0x0F)<<0)         )
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Ghoti



Joined: 31 Dec 2005
Posts: 288
PostPosted: Thu Aug 24, 2006 12:16 am    Post subject: Reply with quote
Hi,

thanks for that code the code probebky works but only the color work with me. I guess it is this function which can't handle alpha channels:

Code:
void fillScreenRect(Color color, int x0, int y0, int width, int height)
{
   if (!initialized) return;
   int skipX = PSP_LINE_SIZE - width;
   int x, y;
   Color* data = getVramDrawBuffer() + x0 + y0 * PSP_LINE_SIZE;
   for (y = 0; y < height; y++, data += skipX) {
      for (x = 0; x < width; x++, data++) *data = color;
   }
}

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My PSP games:

Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php
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Insert_witty_name



Joined: 10 May 2006
Posts: 376
PostPosted: Thu Aug 24, 2006 8:57 am    Post subject: Reply with quote
What I'd do is draw a black quad over the screen and then alter then the alpha value of it.

This should work with the graphics.c stuff:

Code:
void FadeScreen(const int FadeInAlphaValue)
{
guStart();
sceGuDisable(GU_TEXTURE_2D);
CSVertex* vertices = (CSVertex*) sceGuGetMemory(2 * sizeof(CSVertex));
          vertices[0].color = GU_RGBA(0, 0, 0, FadeInAlphaValue);
          vertices[0].x = 0;
          vertices[0].y = 0;
          vertices[0].z = 0;
          vertices[1].color = GU_COLOR(0, 0, 0, FadeInAlphaValue);
          vertices[1].x = 480;
          vertices[1].y = 272;
          vertices[1].z = 0;
sceGuDrawArray(GU_SPRITES, GU_COLOR_8888 | GU_VERTEX_16BIT | GU_TRANSFORM_2D, 2, 0, vertices);
sceGuEnable(GU_TEXTURE_2D);
sceGuFinish();
sceGuSync(0, 0);
}


Where CSVertex is:

Code:
typedef struct
{
   unsigned int color;
   short x, y, z;
} CSVertex;


Just pass the alpha value (0-255) to the function.
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Ghoti



Joined: 31 Dec 2005
Posts: 288
PostPosted: Thu Aug 24, 2006 10:04 pm    Post subject: Reply with quote
Hi, i will try that one. My own solution was to create an image and then replace the pixels every loop with a less alpha value but filling the whole picture slows it down alot, now it is only for transition between screen so interaction or anitmation is not neccesary so the slowing doesn't show to the user but i guess this methode is alot quicker i will try this one thanks
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My PSP games:

Boxy II: http://www.ghoti.nl/boxyii.php
Elementals: http://www.ghoti.nl/Elementals.php
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