[graphics] Improve some camera math (#3825)

I finally went through and worked out the math for the camera matrix,
and improved how it works for PC rendering. I was able to finally avoid
the double perspective divide issue, which I always thought would cause
accuracy issues.

This will help tfrag, tie (no envmap), shrub, and hfrag have less
z-fighting in cases where the camera and the thing you're looking at are
pretty close, but the entire level is far from the origin - like jak 3
temple. I was able to modify the camera matrix so we don't have to do
all the weird scaling/addition in the shader.

Here's a screenshot from the temple oracle checkpoint, cropped from 4k.
This used to have a lot of fighting issues.


![image](https://github.com/user-attachments/assets/4e11157f-ccf5-4f14-98a9-4a0b34da0cd2)

It doesn't help issues where the thing you're looking at is very far
away (jak 1 mountains, some jak 2 city stuff). It also doesn't help with
jak's skirt/scarf, since those use a different renderer.

There's definitely more to do here, but this is a good starting point
and proof that I can at least figure out the math.

Co-authored-by: water111 <[email protected]>

game/graphics/opengl_renderer/background/background_common.cpp

@@ -171,6 +171,68 @@ DoubleDraw setup_tfrag_shader(SharedRenderState* render_state, DrawMode mode, Sh
   return draw_settings;
 }
 
+std::array<math::Vector4f, 4> make_new_cam_mat(const math::Vector4f cam_T_w[4],
+                                               const math::Vector4f persp[4],
+                                               float fog_constant,
+                                               float hvdf_z) {
+  // renderers may eventually have tricks to do things in local coordinates - so use the convention
+  // that the shader has already subtracted off the camera translation from the vertex position.
+  // (I think this could help with accuracy too, since you aren't rotating and subtracting two large
+  // vectors that are very close to each other)
+
+  // this is the perspective x-scaling. This is used to map to a 256-pixel buffer.
+  const float game_pxx = persp[0][0];
+  // on PC, OpenGL uses normalized coordinates for drawing, so divide by the pixel width.
+  // in the game, the perspective divide includes a multiplication by the fog constant, for PC,
+  // just include this multiply here so we can let OpenGL do the perspective multiply.
+  const float pc_pxx = fog_constant * game_pxx / 256.f;
+
+  // this is the perspective y-scaling.
+  const float game_pyy = persp[1][1];
+  // same logic as y - there's a later SCISSOR scaling in the shader that expects this ratio.
+  const float pc_pyy = -fog_constant * game_pyy / 128.f;
+
+  // the depth is considered twice. Once, as the value to write into the depth buffer, which is
+  // scaled for PC here:
+  const float depth_scale = fog_constant * persp[2][2] / 8388608;
+
+  // and once as the value used for perspective divide
+  const float game_pzw = persp[2][3];
+  const float game_depth_offset = persp[3][2];
+
+  // set up PC scaling values
+  math::Vector3f persp_scale(pc_pxx, pc_pyy, depth_scale);
+
+  // it turns out that shifting the depth buffer to line up with OpenGL is equivalent to adding
+  // transformed.w * (hvdf_z / 8388608.f - 1.f) to the depth value. We know that w is just depth *
+  // pzw, so we can include the effect here:
+  const float pc_z_offset = (hvdf_z / 8388608.f - 1.f);
+  persp_scale.z() += pc_z_offset * game_pzw;
+
+  std::array<math::Vector4f, 4> result;
+  for (auto& x : result) {
+    x.set_zero();
+  }
+
+  // fill out the upper 3x3 - simply scale the rotation matrix by the perspective scale.
+  for (int row = 0; row < 3; row++) {
+    for (int col = 0; col < 3; col++) {
+      result[row][col] = cam_T_w[row][col] * persp_scale[col];
+    }
+  }
+
+  // fill out the right most column. This converts world-space points to depth for divide, scaled by
+  // pzw. for now, copy the game.
+  for (int row = 0; row < 3; row++) {
+    result[row][3] = cam_T_w[row][2] * game_pzw;
+  }
+
+  // depth buffer offset - now needs to be scaled by the PC depth buffer scaling too
+  result[3][2] = fog_constant * game_depth_offset / 8388608;
+
+  return result;
+}
+
 void first_tfrag_draw_setup(const GoalBackgroundCameraData& settings,
                             SharedRenderState* render_state,
                             ShaderId shader) {
@@ -181,8 +243,36 @@ void first_tfrag_draw_setup(const GoalBackgroundCameraData& settings,
   glUniform1i(glGetUniformLocation(id, "decal"), false);
   glUniform1i(glGetUniformLocation(id, "tex_T0"), 0);
   glUniformMatrix4fv(glGetUniformLocation(id, "camera"), 1, GL_FALSE, settings.camera[0].data());
+
+  auto newcam =
+      make_new_cam_mat(settings.rot, settings.perspective, settings.fog.x(), settings.hvdf_off.z());
+
+  /*
+  fmt::print("camera:\n{}\n{}\n{}\n{}\n", settings.camera[0].to_string_aligned(),
+             settings.camera[1].to_string_aligned(), settings.camera[2].to_string_aligned(),
+             settings.camera[3].to_string_aligned());
+
+  fmt::print("camera2:\n{}\n{}\n{}\n{}\n", newcam[0].to_string_aligned(),
+             newcam[1].to_string_aligned(), newcam[2].to_string_aligned(),
+             newcam[3].to_string_aligned());
+
+  fmt::print("persp:\n{}\n{}\n{}\n{}\n", settings.perspective[0].to_string_aligned(),
+             settings.perspective[1].to_string_aligned(),
+             settings.perspective[2].to_string_aligned(),
+             settings.perspective[3].to_string_aligned());
+  fmt::print("rot:\n{}\n{}\n{}\n{}\n", settings.rot[0].to_string_aligned(),
+             settings.rot[1].to_string_aligned(), settings.rot[2].to_string_aligned(),
+             settings.rot[3].to_string_aligned());
+  fmt::print("ctrans: {}\n", settings.trans.to_string_aligned());
+  fmt::print("hvdf: {}\n", settings.hvdf_off.to_string_aligned());
+  */
+
+  glUniformMatrix4fv(glGetUniformLocation(id, "pc_camera"), 1, GL_FALSE, newcam[0].data());
+
   glUniform4f(glGetUniformLocation(id, "hvdf_offset"), settings.hvdf_off[0], settings.hvdf_off[1],
               settings.hvdf_off[2], settings.hvdf_off[3]);
+  glUniform4f(glGetUniformLocation(id, "cam_trans"), settings.trans[0], settings.trans[1],
+              settings.trans[2], settings.trans[3]);
   glUniform1f(glGetUniformLocation(id, "fog_constant"), settings.fog.x());
   glUniform1f(glGetUniformLocation(id, "fog_min"), settings.fog.y());
   glUniform1f(glGetUniformLocation(id, "fog_max"), settings.fog.z());

game/graphics/opengl_renderer/shaders/hfrag.vert

@@ -6,7 +6,8 @@ layout (location = 2) in ivec2 uv;
 layout (location = 3) in int vi;
 
 uniform vec4 hvdf_offset;
-uniform mat4 camera;
+uniform vec4 cam_trans;
+uniform mat4 pc_camera;
 uniform float fog_constant;
 uniform float fog_min;
 uniform float fog_max;
@@ -25,27 +26,14 @@ void main() {
   tex_coord.x = (uv.x == 1) ? 1.f : 0.f;
   tex_coord.y = (uv.y == 1) ? 1.f : 0.f;
 
-  vec4 transformed = -camera[3];
-  transformed -= camera[0] * 32768.f * vx;
-  transformed -= camera[1] * position_in;
-  transformed -= camera[2] * 32768.f * vz;
-
-  float Q = fog_constant / transformed.w;
-
-   fogginess = 255 - clamp(-transformed.w + hvdf_offset.w, fog_min, fog_max);
-
-  transformed.xyz *= Q;
-  // offset
-  transformed.xyz += hvdf_offset.xyz;
-  // correct xy offset
-  transformed.xy -= (2048.);
-  // correct z scale
-  transformed.z /= (8388608);
-  transformed.z -= 1;
-  // correct xy scale
-  transformed.x /= (256);
-  transformed.y /= -(128);
-  transformed.xyz *= transformed.w;
+  vec3 vert = position_in - cam_trans.xyz;
+  vec4 transformed = -pc_camera[3];
+  transformed -= pc_camera[0] * (32768.f * vx - cam_trans.x);
+  transformed -= pc_camera[1] * (position_in - cam_trans.y);
+  transformed -= pc_camera[2] * (32768.f * vz - cam_trans.z);
+
+  fogginess = 255 - clamp(-transformed.w + hvdf_offset.w, fog_min, fog_max);
+
   // scissoring area adjust
   transformed.y *= SCISSOR_ADJUST * HEIGHT_SCALE;
   gl_Position = transformed;

game/graphics/opengl_renderer/shaders/merc2.vert

@@ -56,17 +56,6 @@ maddz.xyzw vf26, vf28, vf25
 ```
 */
 void main() {
-  //  vec4 transformed = -perspective3.xyzw;
-  //  transformed += -perspective0 * position_in.x;
-  //  transformed += -perspective1 * position_in.y;
-  //  transformed += -perspective2 * position_in.z;
-
-
-  //  vec4 transformed = -hmat3.xyzw;
-  //  transformed += -hmat0 * position_in.x;
-  //  transformed += -hmat1 * position_in.y;
-  //  transformed += -hmat2 * position_in.z;
-
   vec4 p = vec4(position_in, 1);
   vec4 vtx_pos = -bones[mats[0]].X * p * weights_in[0];
   vec3 rotated_nrm = bones[mats[0]].R * normal_in * weights_in[0];

game/graphics/opengl_renderer/shaders/shrub.vert

@@ -11,6 +11,8 @@ uniform float fog_constant;
 uniform float fog_min;
 uniform float fog_max;
 uniform int decal;
+uniform vec4 cam_trans;
+uniform mat4 pc_camera;
 uniform sampler1D tex_T10; // note, sampled in the vertex shader on purpose.
 
 out vec4 fragment_color;
@@ -33,31 +35,15 @@ void main() {
   // the itof0 is done in the preprocessing step.  now we have floats.
 
   // Step 3, the camera transform
-  vec4 transformed = -camera[3];
-  transformed -= camera[0] * position_in.x;
-  transformed -= camera[1] * position_in.y;
-  transformed -= camera[2] * position_in.z;
-
-  // compute Q
-  float Q = fog_constant / transformed.w;
+  vec3 vert = position_in - cam_trans.xyz;
+  vec4 transformed = -pc_camera[3];
+  transformed -= pc_camera[0] * vert.x;
+  transformed -= pc_camera[1] * vert.y;
+  transformed -= pc_camera[2] * vert.z;
 
   // do fog!
   fogginess = 255 - clamp(-transformed.w + hvdf_offset.w, fog_min, fog_max);
 
-  // perspective divide!
-  transformed.xyz *= Q;
-  // offset
-  transformed.xyz += hvdf_offset.xyz;
-  // correct xy offset
-  transformed.xy -= (2048.);
-  // correct z scale
-  transformed.z /= (8388608);
-  transformed.z -= 1;
-  // correct xy scale
-  transformed.x /= (256);
-  transformed.y /= -(128);
-  // hack
-  transformed.xyz *= transformed.w;
   // scissoring area adjust
   transformed.y *= SCISSOR_ADJUST * HEIGHT_SCALE;
   gl_Position = transformed;

game/graphics/opengl_renderer/shaders/tfrag3.vert

@@ -5,6 +5,8 @@ layout (location = 1) in vec3 tex_coord_in;
 layout (location = 2) in int time_of_day_index;
 
 uniform vec4 hvdf_offset;
+uniform vec4 cam_trans;
+uniform mat4 pc_camera;
 uniform mat4 camera;
 uniform float fog_constant;
 uniform float fog_min;
@@ -31,32 +33,18 @@ void main() {
 
   // the itof0 is done in the preprocessing step.  now we have floats.
 
-  // Step 3, the camera transform
-  vec4 transformed = -camera[3];
-  transformed -= camera[0] * position_in.x;
-  transformed -= camera[1] * position_in.y;
-  transformed -= camera[2] * position_in.z;
 
-  // compute Q
-  float Q = fog_constant / transformed.w;
+  // Step 3, the camera transform
+  vec3 vert = position_in - cam_trans.xyz;
+  vec4 transformed = -pc_camera[3];
+  transformed.w = 0;
+  transformed -= pc_camera[0] * vert.x;
+  transformed -= pc_camera[1] * vert.y;
+  transformed -= pc_camera[2] * vert.z;
 
   // do fog!
   fogginess = 255 - clamp(-transformed.w + hvdf_offset.w, fog_min, fog_max);
 
-  // perspective divide!
-  transformed.xyz *= Q;
-  // offset
-  transformed.xyz += hvdf_offset.xyz;
-  // correct xy offset
-  transformed.xy -= (2048.);
-  // correct z scale
-  transformed.z /= (8388608);
-  transformed.z -= 1;
-  // correct xy scale
-  transformed.x /= (256);
-  transformed.y /= -(128);
-  // hack
-  transformed.xyz *= transformed.w;
   // scissoring area adjust
   transformed.y *= SCISSOR_ADJUST * HEIGHT_SCALE;
   gl_Position = transformed;