How to setup BGFX for 2D rendering

[slewicki]

I have followed a brief tutorial on how to get BGFX setup from Sandeep's blog post and was able to get a basic quad rendered onto the screen with the shader he used as an example. What I am trying to do is to convert his example from a 3D projection into 2D. I am trying to pull some functionality from the fonts example as I see that it is using an Ortho projection, but I am unable to see anything getting rendered. I've done the following changes from his example:

Changed the view setup from:

const bx::Vec3 at  = { 0.0f, 0.0f,   0.0f };
const bx::Vec3 eye = { 0.0f, 0.0f, 10.0f };

float view[16];
bx::mtxLookAt(view, eye, at);

to

const bx::Vec3 at  = { 0.0f, 0.0f,  0.0f };
const bx::Vec3 eye = { 0.0f, 0.0f, -1.0f };

float view[16];
bx::mtxLookAt(view, eye, at);

Changed projection setup from:

float proj[16];
bx::mtxProj(proj, 60.0f, float(WIDTH)/float(HEIGHT), 0.1f, 100.0f, bgfx::getCaps()->homogeneousDepth);

bgfx::setViewTransform(0, view, proj);

// Set view 0 default viewport.
bgfx::setViewRect(0, 0, 0, WIDTH, HEIGHT);

to

float proj[16];
bx::mtxOrtho(proj, 0.0f, WIDTH, 0.0f, HEIGHT, 0.0f, 100.0f, 0.0f, bgfx::getCaps()->homogeneousDepth);
bgfx::setViewTransform(0, view, proj);
bgfx::setViewRect(0, 0, 0, WIDTH, HEIGHT );

I've also tried to keep and remove the float mtx[16]; that was being used to no avail. Any advice on what I may be missing or links to some 2D rendering guides other than the font example would be greatly appreciated.

Thanks in advance

[pezcode]

Your quad is most likely getting culled because you're looking at it from the opposite side (eye.z changed from 10 to -1). BGFX_STATE_DEFAULT implies clockwise culling, you can either turn off all culling or flip it to counter-clockwise:

// turn culling off
BGFX_STATE_DEFAULT & ~BGFX_STATE_CULL_MASK
// counter-clockwise
(BGFX_STATE_DEFAULT & ~BGFX_STATE_CULL_MASK) | BGFX_STATE_CULL_CCW

[slewicki]

This didn't seem to work as I tried both disabling the culling completely and keeping the eye.z value at 10. In both cases I was met with a blank screen, but changing from getting an Ortho matrix to a Proj matrix brings the quad back into view.

[pezcode]

• Is your quad placed at the origin? Your orthographic projection only covers a quarter of the screen since your left/bottom values are 0
• How large is your quad? You're projecting WIDTH units worth of world space into the screen, your quad is possibly just too small to be visible

If all else fails, it's RenderDoc time 🤠

[slewicki]

I had 2 issues, one being that my quad was too small, and the other was that I was passing in my width and height values into the mtxOrtho call incorrectly. Afterwards, disabling of the culling mask showed the quad perfectly. Thanks for the help @pezcode