How to use a frame buffer

[gamecoder-nz]

Here is my code

while (!glfwWindowShouldClose(window)) {
        glfwPollEvents();

        bgfx::setViewFrameBuffer(0, m_FrameBuffer);
        const bx::Vec3 at = { 0.0f, 0.0f,  0.0f };
        const bx::Vec3 eye = { 0.0f, 0.0f, -5.0f };
        float view[16];
        bx::mtxLookAt(view, eye, at);
        float proj[16];
        //bx::mtxProj(proj, 60.0f, float(WNDW_WIDTH) / float(WNDW_HEIGHT), 0.1f, 100.0f, bgfx::getCaps()->homogeneousDepth);
        bx::mtxOrtho(proj, -WNDW_WIDTH / 2, WNDW_WIDTH / 2, -WNDW_HEIGHT / 2, WNDW_HEIGHT / 2, -1000, 1000, 0, bgfx::getCaps()->homogeneousDepth);
        bgfx::setViewTransform(0, view, proj);

        bgfx::setVertexBuffer(0, vbh);
        bgfx::setIndexBuffer(ibh);
        bgfx::submit(0, program);
        bgfx::frame();
    }

But I just get a white screen. If I remove the setViewFrameBuffer line it works. What am I missing?

[bkaradzic]

In that code, you render into offscreen frame buffer and then you don't do anything with it... When you remove bgfx::setViewFrame, things are rendered into backbuffer which becomes visible after calling bgfx::frame.

See provided examples (many examples show framebuffer usage):
https://bkaradzic.github.io/bgfx/examples.html#hdr

[gamecoder-nz]

I thought that might be the case. What part specifically should I be looking for in the examples?

[bkaradzic]

bgfx/examples/09-hdr/hdr.cpp

Lines 40 to 96 in adf5c35

	void screenSpaceQuad(float _textureWidth, float _textureHeight, bool _originBottomLeft = false, float _width = 1.0f, float _height = 1.0f)
	{
	if (3 == bgfx::getAvailTransientVertexBuffer(3, PosColorTexCoord0Vertex::ms_layout) )
	{
	bgfx::TransientVertexBuffer vb;
	bgfx::allocTransientVertexBuffer(&vb, 3, PosColorTexCoord0Vertex::ms_layout);
	PosColorTexCoord0Vertex* vertex = (PosColorTexCoord0Vertex*)vb.data;
	const float zz = 0.0f;
	const float minx = -_width;
	const float maxx = _width;
	const float miny = 0.0f;
	const float maxy = _height*2.0f;
	const float texelHalfW = s_texelHalf/_textureWidth;
	const float texelHalfH = s_texelHalf/_textureHeight;
	const float minu = -1.0f + texelHalfW;
	const float maxu = 1.0f + texelHalfW;
	float minv = texelHalfH;
	float maxv = 2.0f + texelHalfH;
	if (_originBottomLeft)
	{
	float temp = minv;
	minv = maxv;
	maxv = temp;
	minv -= 1.0f;
	maxv -= 1.0f;
	}
	vertex[0].m_x = minx;
	vertex[0].m_y = miny;
	vertex[0].m_z = zz;
	vertex[0].m_rgba = 0xffffffff;
	vertex[0].m_u = minu;
	vertex[0].m_v = minv;
	vertex[1].m_x = maxx;
	vertex[1].m_y = miny;
	vertex[1].m_z = zz;
	vertex[1].m_rgba = 0xffffffff;
	vertex[1].m_u = maxu;
	vertex[1].m_v = minv;
	vertex[2].m_x = maxx;
	vertex[2].m_y = maxy;
	vertex[2].m_z = zz;
	vertex[2].m_rgba = 0xffffffff;
	vertex[2].m_u = maxu;
	vertex[2].m_v = maxv;
	bgfx::setVertexBuffer(0, &vb);
	}
	}

[bkaradzic]

See any example referencing that function... It's copying framebuffer into backbuffer.

[gamecoder-nz]

Thank you very much for the quick reply.