Fix incorrect D3D9 blending

[NZJenkins]

imgui only uses texture stage state for stage 0
But any state set in stages >= 1 will affect rendering
Set stage 1 COLOROP to DISABLED, to deactivate stages >= 1

Our rendering was using fixed function and texture stage state - our states in stage 1, 2, and 3 would interfere with imgui rendering, since it intended to use stage 0 only.

https://docs.microsoft.com/en-us/windows/win32/direct3d9/texture-blending-operations-and-arguments

You can disable a texture stage - and any subsequent texture blending stages in the cascade - by setting the color operation for that stage to D3DTOP_DISABLE. Disabling the color operation effectively disables the alpha operation as well. Alpha operations cannot be disabled when color operations are enabled. Setting the alpha operation to D3DTOP_DISABLE when color blending is enabled causes undefined behavior.

[ocornut]

Hello,
I need to confirm exactly what we are fixing and if other state such as ALPHAOP for stage 1 needs explicit setting.

Could you clarify how to "break" rendering without this patch?

If before the call to ImGui_ImplDX9_RenderDrawData() I add, e.g.

g_pd3dDevice->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_MODULATE);
g_pd3dDevice->SetTextureStageState(1, D3DTSS_COLORARG1, D3DTA_TEXTURE);
g_pd3dDevice->SetTextureStageState(1, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
g_pd3dDevice->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
g_pd3dDevice->SetTextureStageState(1, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
g_pd3dDevice->SetTextureStageState(1, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_COLOROP, D3DTOP_MODULATE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_COLORARG1, D3DTA_TEXTURE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_COLORARG2, D3DTA_DIFFUSE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
g_pd3dDevice->SetTextureStageState(2, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);

Without your patch everything renders correctly.

[ocornut]

OK i realized that my example was essentially setting other stage with same settings.
I merged as 8ced415 also added the explicit call for g_pd3dDevice->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTOP_DISABLE);
Thank you!