Try this:
*primary_surface->SetBlittingFlags(primary_surface,
DSBLIT_BLEND_ALPHACHANNEL);*
You might have to remove the calls to SetSrcBlendFunction() and
SetDstBlendFunction().
[]'s
On Thu, Nov 18, 2010 at 5:22 AM, Kelvin Chen <ryu...@gmail.com> wrote:
> Hi, all:
>
> How can I make IDirectFBSurface::blit supporting a transparent background?
> I have tried a lot of methods, but it doesn't work.
>
> Here is my problem.
> 1> draw something to the primary_surface
> 2> create a tempory_surface with transparent background and draw something
> to it
> 3> blit the content of temporary_surface to the pramary_surface, but this
> operation should not erase what primary_surface already have
>
> Here is my code, it doesn't work, I don't know why. The blue rectangle draw
> on the primary_surface will be erased after the blit operation.
>
> Thanks a lot!
>
> #include <iostream>
> #include <directfb.h>
> *using* *namespace* std;
>
> *int* main(*int* argc, *char* *argv[])
> {
> IDirectFB *dfb;
>
> // Initialize DirectFB
> DirectFBInit(&argc, &argv);
> DirectFBCreate(&dfb);
> dfb->SetCooperativeLevel(dfb, DFSCL_FULLSCREEN);
>
>
> // Create primary surface
> IDirectFBSurface *primary_surface;
> DFBSurfaceDescription primary_surface_description;
> primary_surface_description.flags =
> DFBSurfaceDescriptionFlags(DSDESC_CAPS | DSDESC_WIDTH | DSDESC_HEIGHT |
> DSDESC_PIXELFORMAT);
>
> primary_surface_description.caps = DFBSurfaceCapabilities(DSCAPS_PRIMARY
> | DSCAPS_FLIPPING);
> primary_surface_description.pixelformat = DSPF_ARGB;
> primary_surface_description.width = 1280;
> primary_surface_description.height = 800;
>
> dfb->CreateSurface(dfb, &primary_surface_description, &primary_surface);
> // Draw a big blue square
> primary_surface->SetColor(primary_surface, 0x00, 0x00, 0xff, 0xff);
>
> primary_surface->FillRectangle(primary_surface, 50, 50, 600, 600);
> primary_surface->Flip(primary_surface, NULL, DFBSurfaceFlipFlags(0));
> // Sleep 1 seconds to observe the result
>
> sleep(1);
>
> // Create temporary surface
> IDirectFBSurface *temporary_surface;
> DFBSurfaceDescription temporary_surface_description;
> temporary_surface_description.flags =
> DFBSurfaceDescriptionFlags(DSDESC_CAPS | DSDESC_WIDTH | DSDESC_HEIGHT |
> DSDESC_PIXELFORMAT);
>
> temporary_surface_description.caps =
> DFBSurfaceCapabilities(DSCAPS_FLIPPING); // Not primary
> temporary_surface_description.pixelformat = DSPF_ARGB;
> temporary_surface_description.width = 1280;
>
> temporary_surface_description.height = 800;
> dfb->CreateSurface(dfb, &temporary_surface_description,
> &temporary_surface);
> // Clear the background with transparent black
>
> temporary_surface->Clear(temporary_surface, 0, 0, 0, 0);
> temporary_surface->SetColor(temporary_surface, 0, 0, 0, 0);
> temporary_surface->FillRectangle(temporary_surface, 0, 0, 1280, 800);
>
> // Draw a small red square
> temporary_surface->SetColor(temporary_surface, 0xff, 0x00, 0x00, 0xff);
> temporary_surface->FillRectangle(temporary_surface, 0, 0, 200, 200);
>
> temporary_surface->Flip(temporary_surface, NULL, DFBSurfaceFlipFlags(0));
> // Copy the content of the temporary surface to primary surface
> DFBRectangle rect;
> rect.x = 0;
>
> rect.y = 0;
> rect.w = 1280;
> rect.h = 800;
> temporary_surface->SetSrcBlendFunction(temporary_surface, DSBF_SRCALPHA);
> primary_surface->SetDstBlendFunction(primary_surface, DSBF_DESTALPHA);
>
> primary_surface->Blit(primary_surface, temporary_surface, &rect, 0, 0);
> primary_surface->Flip(primary_surface, NULL, DFBSurfaceFlipFlags(0));
> // Sleep 3 seconds to observe the result
>
> // Note that the original blue square is not destroyed
> sleep(3);
>
> temporary_surface->Release(temporary_surface);
> primary_surface->Release(primary_surface);
>
> dfb->Release(dfb);
>
> *return* 0;
> }
>
>
>
>
> --
> Kelvin Chen
>
> _______________________________________________
> directfb-users mailing list
> directfb-users@directfb.org
> http://mail.directfb.org/cgi-bin/mailman/listinfo/directfb-users
>
>
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