DX11 Alpha blending when rendering to a texture - c++

Question

FINAL EDIT:
Resolved... just needed to learn how alpha blending works in-depth. I should have had:
oBlendStateDesc.RenderTarget[a].DestBlendAlpha = D3D11_BLEND_ZERO;
...set to D3D11_BLEND_ONE to preserve the alpha.
When rendering to the backbuffer once the problem would not be noticed as the colours blend normal and that is the final output. When rendering to the texture the same thing applies, just then rendering the texture to the backbuffer the incorrect alpha plays a role in incorrectly blending the texture into the backbuffer.
I then ran into another issue where the alpha seemed to be decreasing. This is because the colour is blended twice, for example...
Source.RBGA = 1.0f, 0.0f, 0.0f, 0.5f
Dest.RGBA = 0.0f, 0.0f, 0.0f, 0.0f
Render into texture...
Result.RGB = Source.RBG * Source.A + Dest.RGB * (1 - Source.A) = 0.5f, 0.0f, 0.0f
Result.A = Source.A * 1 + Dest.A * 1 = 0.5f
Now...
Source.RBGA = 0.5f, 0.0f, 0.0f, 0.5f
Dest.RGBA = 0.0f, 0.0f, 0.0f, 0.0f
Render into backbuffer...
Result.RGB = Source.RBG * Source.A + Dest.RGB * (1 - Source.A) = 0.25f, 0.0f, 0.0f
Result.A = Source.A * 1 + Dest.A * 1 = 0.5f
To resolve this, when rendering the texture into the backbuffer I use the same blendstate but change the SrcBlend to D3D11_BLEND_ONE so the colour is not blended twice.
Hopefully this helps anyone else having a similar problem....
EDITEND
To increase performance I'm attempting to render a string of text that never changes into a texture to save rendering each individual character every time.
Since I'm rendering strictly in 2D, I've disabled the depth & stencil testing while enabling alpha blending.
Problem is there doesn't seem to be any alpha blending happening, whatever is drawn last overwrites the current pixel with its own data... no blending.
I use a single blend state which I do not change. When rendering to the backbuffer the blending works fine. When rendering the final texture to the backbuffer the blending also works fine. It's just when I render to the texture that blending seems to fail.
Here's how I set up my single blend state:
D3D11_BLEND_DESC oBlendStateDesc;
oBlendStateDesc.AlphaToCoverageEnable = 0;
oBlendStateDesc.IndependentBlendEnable = 0; //set to false, dont need loop below... but just incase
for (unsigned int a = 0; a < 8; ++a)
{
oBlendStateDesc.RenderTarget[a].BlendEnable = 1;
oBlendStateDesc.RenderTarget[a].SrcBlend = D3D11_BLEND_SRC_ALPHA;
oBlendStateDesc.RenderTarget[a].DestBlend = D3D11_BLEND_INV_SRC_ALPHA;
oBlendStateDesc.RenderTarget[a].BlendOp = D3D11_BLEND_OP_ADD;
oBlendStateDesc.RenderTarget[a].SrcBlendAlpha = D3D11_BLEND_ONE;
oBlendStateDesc.RenderTarget[a].DestBlendAlpha = D3D11_BLEND_ZERO;
oBlendStateDesc.RenderTarget[a].BlendOpAlpha = D3D11_BLEND_OP_ADD;
oBlendStateDesc.RenderTarget[a].RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_ALL;
}
// Create the blend state from the description
HResult = m_poDevice->CreateBlendState(&oBlendStateDesc, &m_poBlendState_Default);
m_poDeviceContext->OMSetBlendState(m_poBlendState_Default, nullptr, 0xffffff);
Are there any extra steps I am missing to enable blending when rendering to a texture?
EDIT: If I set AlphaToCoverageEnable to true it blends, but looks terrible. That at least confirms it is using the same blend state... just works differently depending on when rendering to backbuffer or a texture : / Here's my texture desc...
m_oTexureDesc.Width = a_oDesc.m_uiWidth;
m_oTexureDesc.Height = a_oDesc.m_uiHeight;
m_oTexureDesc.MipLevels = 1;
m_oTexureDesc.ArraySize = 1;
m_oTexureDesc.Format = DXGI_FORMAT_R32G32B32A32_FLOAT;
m_oTexureDesc.SampleDesc.Count = 1; //No sampling
m_oTexureDesc.SampleDesc.Quality = 0;
m_oTexureDesc.Usage = D3D11_USAGE_DEFAULT; //GPU writes & reads
m_oTexureDesc.BindFlags = D3D11_BIND_RENDER_TARGET | D3D11_BIND_SHADER_RESOURCE;
m_oTexureDesc.CPUAccessFlags = 0;
m_oTexureDesc.MiscFlags = 0;
EDIT:
Here's some visualization...
Rendering to backbuffer - AlphaBlending enabled.
Rendering to texture - AlphaBlending enabled.
Rendering to backbuffer - AlphaBlending disabled.
Letter T taken from the font file
*When rendering with AB disabled, the letters match exactly (compare 4 & 3)
*When rendering to the backbuffer with AB enabled, the letters render slightly (hardly noticeable) washed out but still blend (compare 4 & 1)
*When rendering to a texture with AB enabled, the letters render even more noticeably washed out while not blending at all. (compare 4 & 2)
Not sure why the colours are washed out with alpha blending enabled... but maybe its a clue?
EDIT:
If I clear the render target texture to say... 0.0f, 0.0f, 1.0f, 1.0f (RGBA, blue)... this is the result:
Only the pixels with alpha > 0.0f & < 1.0f blend with the colour. Another clue but I have no idea how to resolve this issue...