How to update Texture2D in pixel shader every frame (in D3D10)?

Question

Using D3D10, I am drawing a 2d rectangle and want to fill it with a texture (bitmap) that should change a few times every second (like displaying video).

I am using a shader effect, with a Texture2D variable, and trying to update a ID3D10EffectShaderResourceVariable and redraw the mesh.

My actual usage will be by copying bitmaps from memory, and using UpdateSubresource. But it did not work, so I reduced it to test switching between two DDS images. The result is that it draws the first image as expected, but keeps drawing it instead of switching between the two images.

I am new to D3D. Can you explain if this method can work at all, or suggest the right way to do it.

The shader effect:

Texture2D txDiffuse;
SamplerState samLinear
{
    Filter = MIN_MAG_MIP_LINEAR;
    AddressU = Wrap;
    AddressV = Wrap;
};
struct VS_INPUT
{
    float4 Pos : POSITION;
    float2 Tex : TEXCOORD;
};
struct PS_INPUT
{
    float4 Pos : SV_POSITION;
    float2 Tex : TEXCOORD0;
};
PS_INPUT VS( VS_INPUT input )
{
    PS_INPUT output = (PS_INPUT)0;
    output.Pos = input.Pos;
    output.Tex = input.Tex;    
    return output;
}
float4 PS( PS_INPUT input) : SV_Target
{
    return txDiffuse.Sample( samLinear, input.Tex );
}
technique10 Render
{
    pass P0
    {
        SetVertexShader( CompileShader( vs_4_0, VS() ) );
        SetGeometryShader( NULL );
        SetPixelShader( CompileShader( ps_4_0, PS() ) );
    }
}

Code (skipped many parts):

ID3D10ShaderResourceView*           g_pTextureRV = NULL;
ID3D10EffectShaderResourceVariable* g_pDiffuseVariable = NULL;

D3DX10CreateEffectFromResource(gInstance, MAKEINTRESOURCE(IDR_RCDATA1), NULL, NULL, NULL, "fx_4_0", dwShaderFlags, 0, device, NULL, NULL, &g_pEffect, NULL, NULL);

g_pTechnique = g_pEffect->GetTechniqueByName( "Render" );
g_pDiffuseVariable = g_pEffect->GetVariableByName( "txDiffuse" )->AsShaderResource();

// this part is called on Frame render:

device->CreateRenderTargetView( backBuffer, NULL, &rtView);
device->ClearRenderTargetView( rtView, ClearColor );

if(g_pTextureRV != NULL) {
    g_pTextureRV->Release();
    g_pTextureRV = NULL;
}

D3DX10CreateShaderResourceViewFromFile(device, pCurrentDDSFilePath, NULL, NULL, &g_pTextureRV, NULL );
g_pDiffuseVariable->SetResource( g_pTextureRV );

D3D10_TECHNIQUE_DESC techDesc;
g_pTechnique->GetDesc( &techDesc );
for( UINT p = 0; p < techDesc.Passes; ++p )
{
    g_pTechnique->GetPassByIndex( p )->Apply( 0 );
    direct2dDrawingContext->dev->Draw( 6, 0 );
}

// ... present the current back buffer 

Answer 1

One solution, not necessarily the best, but one that doesn't use custom shaders, follows (I wrote it in C# / Managed DirectX but it should be easy to transcode.)

Bitmap bmp; //the bitmap that you will use to update the texture
Texture tex; //the texture that DirectX will render

void Render()
{
  //render some stuff

  bmp = GetNextTextureFrame(); //whatever you do to update your bitmap
  Surface s = tex.GetSurfaceLevel(0);
  Graphics g = s.GetGraphics();
  //IntPtr hdc = g.GetHdc();
  //BitBlt(hdc, 0, 0, bmp.Width, bmp.Height, bmpHdc, 0, 0, 0xcc0020);
  g.DrawImageUnscaled(bmp, 0, 0);
  g.ReleaseHdc(hdc);
  s.ReleaseGraphics();
  device.SetTexture(0, tex);
  //now render your primitives

  //render some more stuff
  //present
}

The commented out lines are the way I actually did it, using an hBitmap and DC with BitBlt, because it's faster than GDI+. A lot of people will probably tell you that the above is a bad way to do it, because of all the memory locking that has to occur, and they're probably right. But I was able to achieve 30fps with multiple 1920x1080 textures, so regardless of whether it's proper, it works.