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DX11 Sprite Rendering Position Problem.

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chowarth    516

I've been trying to implement sprites and read through the RasterTek tutorial on rendering sprites. I got everything working fine but I didn't like the idea of using dynamic vertex buffers to make it possible to move a sprite, so I went about changing them to use a matrix instead.


I have come across a little problem with sprite positions.


I create a few sprites like so:

mpScene->AddSprite( "TestSprite1", "alpha.png", 0,    0,    100,    100 );
mpScene->AddSprite( "TestSprite2", "alpha.png", 100,    0,    100,    100 );
mpScene->AddSprite( "TestSprite3", "alpha.png", 0,      100,    100,    100 );


Now my assumption is that if I create a sprite at (0, 0) with dimensions of (100, 100), and then create another at (100, 0) with the same dimensions that the two sprites would be right next to each other, however they seem to be the full width of a sprite apart:





This is how I create my sprite buffers:

// Calculate screen space positions of the vertices
float left        = ( ( screenWidth * 0.5f ) * -1 ) + posX;
float right        = left + width;
float top        = ( screenHeight * 0.5f ) + posY;
float bottom    = top - height;

// Populate vertices.
vertices[0].Pos = XMFLOAT3( left, top, 1.0f );
vertices[0].Tex = XMFLOAT2( 0.0f, 0.0f );

vertices[1].Pos = XMFLOAT3( right, top, 1.0f );
vertices[1].Tex = XMFLOAT2( 1.0f, 0.0f );

vertices[2].Pos = XMFLOAT3( right, bottom, 1.0f );
vertices[2].Tex = XMFLOAT2( 1.0f, 1.0f );

vertices[3].Pos = XMFLOAT3( left, bottom, 1.0f );
vertices[3].Tex = XMFLOAT2( 0.0f, 1.0f );

// Create indices array.
indices = new USHORT[numIndices];
indices[0] = 0;    //
indices[1] = 1;    // Triangle 1
indices[2] = 2;    //___________
indices[3] = 0;    //
indices[4] = 2;    // Triangle 2
indices[5] = 3;    //


and how I create the sprite matrix:

XMMATRIX p    = XMMatrixTranslation( mPosition.x, mPosition.y, mPosition.z );
XMMATRIX r    = XMMatrixRotationZ( mRotation );
XMMATRIX s    = XMMatrixScaling( mScale.x, mScale.y, 1.0f );

XMStoreFloat4x4( &mMatrix, p * r * s );


and the rendering of the sprites:

// Disable depth testing when drawing sprite objects.
pDevice->SetDepthStencilState( mpDepthDisabledState );

mpSpriteFX->SetMatrix( "gViewProjMatrix", pCamera->GetOrthoMatrix() );
pDevice->SetInputLayout( mpSpriteFX->GetInputLayout() );

CSprite* pSprite = NULL;

while( ( pSprite = pSpriteList->EnumAsset() ) != 0 )
    CTexture* pTexture = pTextureList->GetAsset( pSprite->GetTextureUID() );
    mpSpriteFX->SetSRV( "dTexture", pTexture->GetSRV() );

    pDevice->SetVertexIndexBuffer( sizeof( SpriteVertex ), pSprite->GetVB(), pSprite->GetIB() );

    mpSpriteFX->SetMatrix( "gWorldMatrix", pSprite->GetMatrix() );

    UINT numPasses = mpSpriteFX->GetNumPasses();
    for( UINT pass = 0; pass < numPasses; pass++ )
        pDevice->ApplyTechPass( mpSpriteFX->GetTechnique(), pass );

        pDevice->DrawIndexed( mNumIndices, 0, 0 );
// Re-enable depth testing for drawing non-sprite objects.
pDevice->SetDepthStencilState( NULL );


I'm just wondering if there's something I've done wrong or an explanation as to why the sprites would be positioned the full width of a sprite apart instead of next to each other as I would expect.


Thanks in advance.



Appears the image wasn't working :( Fixed (I hope).

Edited by chowarth

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