radiantwave-legacy/internal/graphics/virtual_framebuffer.go

package graphics

import (
	"fmt"

	"github.com/go-gl/gl/v3.3-core/gl"
)

const (
	VirtualWidth  int32 = 1920
	VirtualHeight int32 = 1080
)

var (
	vfbo             uint32
	vfboTexture      uint32
	vfboDepthStencil uint32
	blitVAO          uint32
	blitVBO          uint32
	blitShaderProg   uint32
	nativeW, nativeH int32
)

// InitVirtualFramebuffer creates the FBO at virtual resolution and the blit shader.
// Call after OpenGL context is created.
func InitVirtualFramebuffer(displayW, displayH int32) error {
	nativeW = displayW
	nativeH = displayH

	// --- FBO setup ---
	gl.GenFramebuffers(1, &vfbo)
	gl.BindFramebuffer(gl.FRAMEBUFFER, vfbo)

	gl.GenTextures(1, &vfboTexture)
	gl.BindTexture(gl.TEXTURE_2D, vfboTexture)
	gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA8, VirtualWidth, VirtualHeight, 0, gl.RGBA, gl.UNSIGNED_BYTE, nil)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
	gl.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, vfboTexture, 0)

	// Depth/stencil renderbuffer
	gl.GenRenderbuffers(1, &vfboDepthStencil)
	gl.BindRenderbuffer(gl.RENDERBUFFER, vfboDepthStencil)
	gl.RenderbufferStorage(gl.RENDERBUFFER, gl.DEPTH24_STENCIL8, VirtualWidth, VirtualHeight)
	gl.FramebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_STENCIL_ATTACHMENT, gl.RENDERBUFFER, vfboDepthStencil)

	if status := gl.CheckFramebufferStatus(gl.FRAMEBUFFER); status != gl.FRAMEBUFFER_COMPLETE {
		return fmt.Errorf("virtual framebuffer incomplete: 0x%X", status)
	}

	gl.BindFramebuffer(gl.FRAMEBUFFER, 0)

	// --- Fullscreen quad ---
	vertices := []float32{
		// pos (x,y)   texcoord (u,v)
		-1, -1, 0, 0,
		1, -1, 1, 0,
		-1, 1, 0, 1,
		1, 1, 1, 1,
	}

	gl.GenVertexArrays(1, &blitVAO)
	gl.GenBuffers(1, &blitVBO)
	gl.BindVertexArray(blitVAO)
	gl.BindBuffer(gl.ARRAY_BUFFER, blitVBO)
	gl.BufferData(gl.ARRAY_BUFFER, len(vertices)*4, gl.Ptr(vertices), gl.STATIC_DRAW)

	gl.EnableVertexAttribArray(0)
	gl.VertexAttribPointerWithOffset(0, 2, gl.FLOAT, false, 4*4, 0)
	gl.EnableVertexAttribArray(1)
	gl.VertexAttribPointerWithOffset(1, 2, gl.FLOAT, false, 4*4, 2*4)

	gl.BindVertexArray(0)

	// --- Blit shader ---
	var err error
	blitShaderProg, err = compileBlitShader()
	if err != nil {
		return fmt.Errorf("blit shader compilation failed: %w", err)
	}

	return nil
}

// BeginVirtualRender binds the FBO so all subsequent draws go to the virtual 1080p buffer.
func BeginVirtualRender() {
	gl.BindFramebuffer(gl.FRAMEBUFFER, vfbo)
	gl.Viewport(0, 0, VirtualWidth, VirtualHeight)
}

// BlitToScreen draws the virtual buffer to the actual screen at native resolution.
func BlitToScreen() {
	gl.BindFramebuffer(gl.FRAMEBUFFER, 0)
	gl.Viewport(0, 0, nativeW, nativeH)
	gl.ClearColor(0, 0, 0, 1)
	gl.Clear(gl.COLOR_BUFFER_BIT)

	gl.UseProgram(blitShaderProg)
	gl.ActiveTexture(gl.TEXTURE0)
	gl.BindTexture(gl.TEXTURE_2D, vfboTexture)

	gl.BindVertexArray(blitVAO)
	gl.DrawArrays(gl.TRIANGLE_STRIP, 0, 4)
	gl.BindVertexArray(0)
}

// DestroyVirtualFramebuffer cleans up all FBO resources.
func DestroyVirtualFramebuffer() {
	if blitShaderProg != 0 {
		gl.DeleteProgram(blitShaderProg)
	}
	if blitVBO != 0 {
		gl.DeleteBuffers(1, &blitVBO)
	}
	if blitVAO != 0 {
		gl.DeleteVertexArrays(1, &blitVAO)
	}
	if vfboDepthStencil != 0 {
		gl.DeleteRenderbuffers(1, &vfboDepthStencil)
	}
	if vfboTexture != 0 {
		gl.DeleteTextures(1, &vfboTexture)
	}
	if vfbo != 0 {
		gl.DeleteFramebuffers(1, &vfbo)
	}
}

func compileBlitShader() (uint32, error) {
	vertSrc := `#version 330 core
layout(location = 0) in vec2 aPos;
layout(location = 1) in vec2 aTexCoord;
out vec2 vTexCoord;
void main() {
    vTexCoord = aTexCoord;
    gl_Position = vec4(aPos, 0.0, 1.0);
}` + "\x00"

	fragSrc := `#version 330 core
in vec2 vTexCoord;
out vec4 FragColor;
uniform sampler2D screenTexture;
void main() {
    FragColor = texture(screenTexture, vTexCoord);
}` + "\x00"

	vertShader, err := compileShader(vertSrc, gl.VERTEX_SHADER)
	if err != nil {
		return 0, err
	}
	fragShader, err := compileShader(fragSrc, gl.FRAGMENT_SHADER)
	if err != nil {
		return 0, err
	}

	prog := gl.CreateProgram()
	gl.AttachShader(prog, vertShader)
	gl.AttachShader(prog, fragShader)
	gl.LinkProgram(prog)

	var status int32
	gl.GetProgramiv(prog, gl.LINK_STATUS, &status)
	if status == gl.FALSE {
		var logLen int32
		gl.GetProgramiv(prog, gl.INFO_LOG_LENGTH, &logLen)
		logStr := make([]byte, logLen)
		gl.GetProgramInfoLog(prog, logLen, nil, &logStr[0])
		return 0, fmt.Errorf("shader link error: %s", string(logStr))
	}

	gl.DeleteShader(vertShader)
	gl.DeleteShader(fragShader)
	return prog, nil
}

func compileShader(src string, shaderType uint32) (uint32, error) {
	shader := gl.CreateShader(shaderType)
	csrc, free := gl.Strs(src)
	gl.ShaderSource(shader, 1, csrc, nil)
	free()
	gl.CompileShader(shader)

	var status int32
	gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
	if status == gl.FALSE {
		var logLen int32
		gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLen)
		logStr := make([]byte, logLen)
		gl.GetShaderInfoLog(shader, logLen, nil, &logStr[0])
		return 0, fmt.Errorf("shader compile error: %s", string(logStr))
	}
	return shader, nil
}